04 GMC Yukon XL... Dex III or Dex IV?

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I am getting ready to do a fluid exchange and filter change on my 04 Yukon 2500 with the 6.0/4L80 combo. My manual states Dex III, but I see a lot of reviews here tell folks to use the Dex IV in the same tranny. Which one should I be using? The truck has just shy of 100K. I don't know what the difference is between the fluids. I have searched a lot and am still confused.

I love these trucks, I have a 00 2500 Silverado with 200K and its still running strong! (same 6.0/4L80 combo)

Thanks for the help.
 
I'd either run DexVI or Amsoil and call it a day. Dex VI is the latest Dex standard and it is a stable, robust fluid. The Amsoil is on-par--- I believe the Dex VI equivalent is the "Low Viscosity" offering from Amsoil.
 
Dex III is obsolete. Dex VI is a more shear-resistant, stronger fluid with a longer service life and usually improved function, especially in newer transmissions (probably because it shears less).
 
Yes - go with DEX VI in your application.

The DEX VI engineering specs require that fluid to have approximately 2x more vis stability and 2x the oxidation resistance over the former fluid. In theory, you could easily run DEX VI twice as long as DEX III. UOAs show these DEX VI products to be excellent and robust.

Any product that meets the specs, and is licensed, is a viable choice. The DEX VI criteria is very strict in that it has both performance attributes, and also chemistry package requirements that necessitate a very specific additive package be used. Therefore, any licensed product is going to be very good. Hence, consider any house brand, something like the Wallyworld ST DEX VI as it is a licensed product, and very cost effective.
 
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Dex VI. I have a 2004 5.3L and Dex VI improved shifting quite a bit. I went with it at about 50,000mi I think and still have it at 125,000 now. May do 1 more flush while I own truck.
 
Oops I was wrong above. I did go to Dex 6 at 50k but then had it flushed again at 120k with Dex 6. Still shifting great and I am good to go until I sell/trade it.
 
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I use supertech dex 6 in my 4T65e. Its a much better product than dex 3 of the model year.

You could also consider Mobil D/M (dex merc) which is the only product sold in the states they carries the Allison certification which is the best dex/merc imo. Its available at Target.

Also max life would work in this application, it has more shear resistance than older dex 3h but it's all depending on what's available. You certainly have more than one choice just so you know.
 
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