GMT800 vs GMT900. Which to buy?

[Redfish5050]

Hello all,

I'm in the market to upgrade my current daily, a 05 Highlander with either a 800 or 900 Yukon Denali/SLT though unsure which would be better overall for reliability and dependability. While I'm not scared to buy a higher mileage one with good service records and am aware that typically with higher mileage ones I'll be looking at expensive repairs (suspension, timing chain, control arms, etc) I'm unsure which generation would be better. One issue that I'll run into with either vehicle would be northeastern rusting issues and also navigating it through NY streets but I'll adapt. I do drive around 12-14k miles a year and would love a big cruiser on the highway. I am somewhat mechanically inclined and can wrench on some basic things.

GMT800: Definitely the more basic of the two generations though the suspect nature of the 4L65 leaves much to be desired of. Typically more higher mileage and more likely to run across beaten up examples than relatively clean. That being said, I do have a soft spot for this generation. One pro of this generation would be not having AFM.

GMT900: Much more luxury focus with so much more amenities than the 800 (backup cam, heated/ventilated seats, higher quality interior). The 6L80 isn't that bad (?) at least compared to the 4L65 which isn't saying much. But the big boogy man of this generation is the introduction of AFM which GM ruined a perfectly bulletproof, stout and workhorse engine to a lifter waiting to collapse (damn you EPA). Could find cleaner examples though but at a much higher premium. While I am aware there are tunes/chips that disable the AFM, I have heard the lifters do have a potential to fail.

Thoughts/opinions/advice?

I just bought a 2016 Tahoe with 80k miles. The AFM is easy and simple to overcome in any vehicle. Go to RangeTechnology.com or HollyPerformance.com.

The 6L80 transmission is definitely a liability. When you test drive the vehicle, put it in trailer tow mode at the end of the drive to check the transmission temperature. If it’s up around 190°, not good, but you can still go ahead and replace the transmission thermostat with GM’s new 150° version.

My transmission was shuttering around 40-50 mph consistently. Found a good old rebuild shop, and did a full rebuild which included miscellaneous upgrade kits. They said high temps deteriorate a transmission, but kept reiterating that the AFM is equally harmful to the transmission fluid pump.

Also, consider a Catch Can since either vehicle will be a GDI (gasoline direct injection) engine. This will preserve the intake valves. Check out Tracy Lewis, and UPR Products for catch cans.

All of the above is on YouTube. This should put you pretty close to bulletproof. Best of luck to you!

 

[ivin74]

Yeah I was considering going out of state for a non-rusty example or an exceptional frame around the tri-state area.

I mean I can find 04-06 Denalis relatively in good condition for around $5k which in a market like this is a steal.

If you do go with the 800 platform, get an 05 or 06. Those model years came out with electric cooling fans.

 

[Redfish5050]

I have a 2007 Tahoe LTZ, 280,000 miles, burns no oil, original 4 speed Transmission (never rebuilt) The only recurring issue I have is the catalytic convertor likes to fail, and no one can diagnose why. I had the rear axle rebuilt at around 200K due to a funny noise. Beyond that it has been a great vehicle.

I’m just guessing here, but is the catalytic converter getting contaminated by oil, etc. from crankcase gases? If so, consider installing a Catch Can.

 

[Marky Dissod]

Although Redfish5050 is wrong about GMT800 or GMT900 having direct injection, he's STILL right about EVERYTHING ELSE.

 

[OR VietVet]

Welcome to the forum.

I own and prefer the 800's. My 05 is a dream and the most comfortable seats I have ever drove in. When I first bout an 02 years ago, I also drove an 07 and an 08 and hated hated hated the seats. I love the 05 Z71 I own, especially after the work I have done to it. Travel to get a lower mileage one and make sure you DO GET service records and stay away from the rust. I have lived and worked in shops where the rust was a major concern. The engine is solid and the transmission will likely have been redone by now, as I will certainly do mine when it happens.

 

[S33k3r]

Although Redfish5050 is wrong about GMT800 or GMT900 having direct injection, he's STILL right about EVERYTHING ELSE.

Dumb question, but have you checked your Os sensors? Maybe nothing is wrong with the catalytic converters 00 maybe it is a sensor issue. You can swap the "bad side" with the "good side", and see if the problem moves.

 

[mountie]

I bought my GMT800 Yukon XL with 140,000 miles..... It has 171,000 now..... It was garage kept, and well serviced. It was a one-owner, and the interior ..... They never drank coffee in it.

A Florida ride.... It was a dealer trade in. Zero rust. Engine- you can eat off of it.. It has been perfect since I bought it 5 years ago.
( OK... I just replaced the altinator last month. ( pic is the day after I bought it... It has Michelins now... 1st thing I bought was a nice dash cover to keep it perfect.
I will NEVER sell it....

 

[mikeyss]

I've owned GMT800 and currently own a GMT900. I agree the rack and pinion steering is nice on the GMT900, but I also like the strut front suspension over the torsion bar set up on the GMT800. But, the 03-06 GMT800 have the BEST seats ever, and the dashes don't crack and fall apart. It's ashame the GMT800 never got a L92/6L80 combo...

 

[Marky Dissod]

... also like the (GMT900) strut front suspension over the torsion bar set up on the GMT800 ... shame the GMT800 never got a L92 / 6L80 combo...

How difficult is it to convert a GMT800 to front struts?
We can pretty easily utilize an L92 / L9H / L94; think Lingenfelter (?) makes a 58x /24x signal converter.
A GMT800 utilizing a 6L80E is a bit more daunting of a task (I do miss the 6L80E in my '12 Yukon XL-SLT) ...

 

[91RS]

How difficult is it to convert a GMT800 to front struts?
We can pretty easily utilize an L92 / L9H / L94; think Lingenfelter (?) makes a 58x /24x signal converter.
A GMT800 utilizing a 6L80E is a bit more daunting of a task (I do miss the 6L80E in my '12 Yukon XL-SLT) ...

You can do Atomic Fab coilovers but you have to cut stuff off the frame to do it so you can’t go back. I don’t feel like you’d want to but just putting it out there.