4L Tranny

[LDMoore]

The Suburban will have AFM, all of the 5.3s and the 6.0 in the 1500s had it. Your trans in the 5.3 likes clean oil and the corvette servo mod. But talk to the guys and search this forum before doing it. @01ssreda4

The 2007-2008s were rated for about 14 city and 20 highway depending on the gearing. Lower gears will yield slightly less highway mileage.

If the engine happens to be the 6.0 L76, it will have the Supermatic 4L70. Oh wait, you said Z71, that was LTZ only if memory serves.

@kbuskill Ken here has an '08 'Burb with about 250K, he can give you better pointers than I too.

Thank you sir! A corvette servo is definitely in the plans but I will look around here a bit and watch some videos before I tackle it

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[LDMoore]

Not really sure what to say...

Keep the transmission fluid changed and clean and add a bigger transmission cooler.

Same for the oil, clean and changed. I run Mobil 1 extended performance 5w30, 15k mile oil.

I run 13k-15k mile OCIs but I have a dual remote mount oil filter setup with filters that are much larger than stock and an oil cooler. Blackstone labs says I could run the oil longer if I chose to.

As far as mileage is concerned... I have 3:73 gears out back with the 4L60E 2wd with the 5.3l AFM disabled in the custom tune, tuned for 89 octane, and I average about 13.5-14 mpg around town and about 18.5-19 mpg on the interstate running 75 mph loaded down with the wife, 3 kids, and the back loaded down with luggage.

My truck is also lowered 4/6 which may improve MPG. Debatable, but thought I would mention it.

I don't think the 6 speed transmissions make that big of a difference as far as fuel mileage is concerned.

Awesome thanks for the tips! I used to have a 1/2 ton pickup with 4l60/3.42s then a 3/4 ton with 4l85/4.10s but that was 8 years ago. Since then I've gotten used to 6 speeds in our Escalade, my Duramax and Camaro. Maybe it's just me but seems like since the 6s came out I've more and more about the limits and unreliability of the 4 speed

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[LDMoore]

I have to add, it screws with me when I drive both vehicles on the same day. I drive a lot in the city, it's crazy how different the 4 speed and 6 speed are. The 6 speed has better ratios and keeps the engine in it's happy place. The 4 speed makes the engine fall on its face at times, especially with the 4.10 rear. If you are going 30mph and drop the hammer, you will NOT get 1st gear because the engine speed is too high. I really wish I could swap a 6L80 in my 06, but the cost wouldn't be worth it.

The last 4 speed I had was a 3/4 ton 6.0 with 4.10s. It would pull like crazy and sounded great with a big block muffler but 14 was as good as I could hope for on the highway. A 6 speed would have done that pickup a lot of good lol

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