Major upgrades GMT800, 06ish XL 2500

lowderkg · Oct 27, 2024

Newbie here. Gonna buy 2003--2006 Yukon XL, SLT W/ 8.1. Once rig here, one of the big "to do" on bucket list is upgrade tyranny to best there is. Forgive my Naiveté as relates to engine/tranny/rear end. But would it be possible to upgrade from 4 speed to like a 5-6 speed, ie 6L90 ? If I have posted this in wrong place, I apologize. I am just on a mission to have a kick butt ride. Thank you for any thoughts and suggestions.
Lowderkg

strutaeng · Oct 27, 2024

I believe the only way to upgrade to the 6 speed on the GMT800 is via a Holley aftermarket ECU and that requires a 58X reluctor wheel on the crankshaft, which means pulling the engine and complete disassemble. This on the LS-based engines, and I'm assuming it still applies to the 8.1 since it's kinda of like a hybrid but still uses LS electronics. Maybe you can call Holley and ask them?

What gears do you have on it? 3.73 or 4.10?

I've toyed with the idea of swapping an 8.1/Allison 5 speed on my project 04 Suburban 2500 6.0/4L80e, but it's just thought at this point.

You can do a supercharger, turbo or something else from Raylar such as a larger bore/stroker/cam/aftermarket heads. Lawrence Tolman has modified a few 8.1s. Check out his channel on YT. That's probably a $8,000-$10,000 upgrade on the NA option.

You can get a lot more power on the turbo (especially if you do the work yourself) for cheaper on a HP/$ ratio, especially with these cheap chicom turbos that are so affordable these days.

Marky Dissod · Oct 27, 2024

lowderkg said:
Gonna buy 03-06 Yukon XL, SLT W/ 8.1L.
Once rig here, one of the big "to do" on bucket list is upgrade tyranny to best there is.
Forgive my Naiveté as relates to engine/tranny/rear end.
But would it be possible to upgrade from 4L80 to like a 5-6 speed, ie 6L90?
If I have posted this in wrong place, I apologize.
I am just on a mission to have a kick butt ride. Thank you for any thoughts and suggestions.

Upgrade tyranny? That kind of political talk can get you summarily banned at this 'forum' - a bit of a weird irony ...
ANYWAY

If your pcm can operate a 6L90 ... actually I THINK the 6L90 requires an ecm for the engine and a tcm for the 6L90?
Meaning you might need a major wiring harness overhaul, maybe a few other modules would need an upgrade.
Involved, but definitely doable.
You may be better off considering the Allison 6speed, the one that lots of people think is a five speed,
but becomes a 6speed after a tune?

What, specifically, do you mean by 'kick @$$ ride'?
Most people who don't know what they're really getting into say, 'x amount of horses',
instead of understanding how quick they want to cover the 1/4 mile, for example.

Are you more interested in towing/hauling strength, instead or high RpM power?
How much further off-road do you want to be able to go?

Define your terms.

mikeyss · Oct 27, 2024

Gen I and II Chevrolet and Buick Engine 6L80E/6L90E 6 Speed Conversion Kit - Zero Gravity Performance

GM Gen 1 and 2 Chevrolet 6L80E 6L90E Conversion Kit. Comes with a 6L80e or 6L90e Transmission Torque Converter, TPS kit and TCM2650 Gateway Module

www.zerogravityperformance.com

Seems the 6L80/6L90 swaps are becoming easier.

Fless · Oct 27, 2024

Welcome to TYF. Moved you here from the 2021+ General Discussion section.

lowderkg · Oct 27, 2024

Marky Dissod said:
Upgrade tyranny? That kind of political talk can get you summarily banned at this 'forum' - a bit of a weird irony ...
ANYWAY

If your pcm can operate a 6L90 ... actually I THINK the 6L90 requires an ecm for the engine and a tcm for the 6L90?
Meaning you might need a major wiring harness overhaul, maybe a few other modules would need an upgrade.
Involved, but definitely doable.
You may be better off considering the Allison 6speed, the one that lots of people think is a five speed,
but becomes a 6speed after a tune?

What, specifically, do you mean by 'kick @$$ ride'?
Most people who don't know what they're really getting into say, 'x amount of horses',
instead of understanding how quick they want to cover the 1/4 mile, for example.

Are you more interested in towing/hauling strength, instead or high RpM power?
How much further off-road do you want to be able to go?

Define your terms.

Oh I so appreciate the replies. After reading, a six speed would not be economically feasible. As to what I will end up within the next 1- 60 days (contingent what on market) as to if it is a 3.73 or a 4.10 is unclear. But I am a buyer either way as I been on look out for a GMX XL 2500, even if it in 25K range. If I could find one that has less than 150,000 miles unmodified, that would be terrific. As suggested, I will look into Mr. Toleman’s posts to gain greater insights. Though I can afford otherwise, I have been driving the same ole’ 2003 Yukon for over 20 years and milked her to 190,000 miles. She has served me well. The bottom line is I am looking for my final ride and will fixed her up as a “kick butt“ ride and install all the upgrades and modifications that gentleman such as you all have done so before. At 60+ years of age, I no speed freak nor a fellow who will be towing 10K, at least not often. Just want to make my last ride the best I can and then pass it down to my son.

As necessary I will have to farm out to those who are mechanically inclined than I. It will be a project I will enjoy. Be it a 3 inch lift, HD breaks/suspension, 2-3 inch lift, mud flaps, tow mirrors, K&N, LED interior, modified head / tails lights, front / rear and God knows what else. As asked by another, my terms are this. Simply want to make a GMT800 into the most perfect ride I can, and gain insights and experiences of those who have done so before me. Aa such, any insights will be welcomed.

Joseph Garcia · Oct 28, 2024

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

You are already receiving sage advice from the knowledgeable folks on this Forum.

S33k3r · Thursday at 12:57 PM

lowderkg said:
Oh I so appreciate the replies. After reading, a six speed would not be economically feasible. As to what I will end up within the next 1- 60 days (contingent what on market) as to if it is a 3.73 or a 4.10 is unclear. But I am a buyer either way as I been on look out for a GMX XL 2500, even if it in 25K range. If I could find one that has less than 150,000 miles unmodified, that would be terrific. As suggested, I will look into Mr. Toleman’s posts to gain greater insights. Though I can afford otherwise, I have been driving the same ole’ 2003 Yukon for over 20 years and milked her to 190,000 miles. She has served me well. The bottom line is I am looking for my final ride and will fixed her up as a “kick butt“ ride and install all the upgrades and modifications that gentleman such as you all have done so before. At 60+ years of age, I no speed freak nor a fellow who will be towing 10K, at least not often. Just want to make my last ride the best I can and then pass it down to my son.

As necessary I will have to farm out to those who are mechanically inclined than I. It will be a project I will enjoy. Be it a 3 inch lift, HD breaks/suspension, 2-3 inch lift, mud flaps, tow mirrors, K&N, LED interior, modified head / tails lights, front / rear and God knows what else. As asked by another, my terms are this. Simply want to make a GMT800 into the most perfect ride I can, and gain insights and experiences of those who have done so before me. Aa such, any insights will be welcomed.

What is the most important modification to you, if I may ask?

Bigburb3500 · Saturday at 2:31 PM

If I may recommend, look at lowering your purchase budget and pull the full engine and do a diesel swap. I think from what I am reading in your post, you want a bulletproof and somewhat-unique truck.
Diesel swapping the 2500 appears to be fairly doable. There is a YouTube channel that did it in the garage at home (non-professional mechanic style - DIY special). That would give you the power and fun factor you are looking for. I used to have an 01 2500 and the engine transmission combo will never give you “excitement.” Do a diesel swap and go crazy with the mods.

Marky Dissod · Saturday at 4:36 PM

lowderkg said:
Simply want to make a GMT800 into the most perfect ride I can ...

Still haven't defined your terms yet. A 'vette is PERFECT for some things, sucks for others.
Same can be said for a 2500 suv.

Bigburb3500 said:
If I may recommend, look at lowering your purchase budget and pull the full engine and do a turbodiesel swap.
I think from what I am reading in your post, you want a bulletproof and somewhat-unique truck.
Turbodiesel swapping the 2500 appears to be fairly doable. There is a YouTube channel that did it in the garage at home (non-professional mechanic style - DIY special).
That would give you the power and fun factor you are looking for. I used to have an 01 2500 and the engine transmission combo will never give you “excitement.”
Do a turbodiesel swap and go crazy with the mods.

A 6.6L DuraMax would be pricey ... but the bang for the buck would be tough to beat, especially
if you figure out how to run it on alternative fuels.

Major upgrades GMT800, 06ish XL 2500

lowderkg

TYF Newbie

strutaeng

Full Access Member

Marky Dissod

Full Access Member

mikeyss

Full Access Member

Gen I and II Chevrolet and Buick Engine 6L80E/6L90E 6 Speed Conversion Kit - Zero Gravity Performance

Fless

lowderkg

TYF Newbie

Joseph Garcia

S33k3r

Full Access Member

Bigburb3500

Senior Member

Marky Dissod

Full Access Member

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