I was wondering about some different transmission fluids ive seen and if they would work in these trucks. If anyone was wondering what the approved transmission fluids from GM are:

http://www.imakenews.com/lubritec/e_article001628035.cfm?x=b11,0,w

"Dextron IV liscensce holders"

FYI, it's Dexron VI...

You can use any Dex III fluid if you don't care about your warranty...

I switched my trans from Dex VI to Dex III at 5k miles. The fluid I'm using is Schaeffer's 204SAT Synthetic ATF.

thanx, deatails, details. i just found the information and figured there might be some others that would wonder the same thing after reading the sticky on the allison fluids

Also any TES295 certified fluid.

TES295 is better stuff than Dex

Check out the sticky on approved Allison Fluids. They have come out with a new schedule, TES 389. I recently changed mine with Shell Donax TX @ $160 for a 5 gallon bucket. It's red and I didn't notice a change, but then again I haven't punch it out yet. I've been limping around with some codes, and the tranny is doing it's own thing. I would have gone with Amsoil, but the representative didn't call be back and I wasn't going to order fluid online. I would have bought Transynd, but they're way too proud of that stuff. There's another Shell product, Castrol, and Mobil on the list. You can check it out at https://fdlrd.swri.org/Allison/ApprovedFluidsList.aspx?Id=2.

TES-389 is a spec for what used to be the DEX III stuff. When GM quit licensing DEX III in 2007, Allison had to create this new spec for people that didn't want to be forced into buying TES-295 fluids. Admittedly, TES-295's are top notch, but they are also top-shelf in price as well. Many people simply have no need for such expensive fluids.

The TES-389 fluids are verified for performance and issued licenses if they meet the criteria. It merely continues the existence of what was essentially DEX III. It also specifically address the seal compatibility issue. Any lincensed TES-389 will not cause seal issues in older Allison trannies, as I understand it. Hence, DEX VI is NOT a TES-389 licensed fluid. TES-389 is an Allison fluid license spec. DEX VI is a GM fluid license spec. They are difference products with difference construction by design.

DEX VI, OTOH, is a significant improvement over DEX III. It has 2x the oxidation and shear resistance. It is a much better fluid than DEX III, but ONLY if you can use it without fear of seal hardening in some transmissions.

GM felt that DEX VI was OK for all backwards compatibility; Allison disagrees. Hence, the serial number cutoffs for the Indy and Baltimore plants. If your truck tranny is after the cutoff, then DEX VI is a perfectly suited fluid for the tranny; not as good as TES-295, but certainly better than former DEX III products.

Allison has but two specs in regard to fluids we'd use; a premium (TES-295) and a basic (TES-389). DEX VI fluids fall in-between those two specs as far as abilities. But because DEX VI cannot pass the TES-295 standards, it gets pushed down to the same service schedule as the TES-389 fluids. But make no mistake, DEX VI can kick the butt of any TES-389 in regard to longevity. If Allison were so inclined to make a third spec, the DEX VI would likely fall in-between the others.

To put it simply, there is a "good, better, best" mentality here. Allison only has the "good" (TES-389) and the "best" (TES-295). They make no acknowledgement of "better", so anything that is "better" than "good" still gets treated (downgraded) as inferior, even though that is not the true view of things.

Transynd synthetic from the Allison dealer, they have the spin on filters as well at a reasonable price. Just be sure to take the magnet off the old filter, clean and install on new filter.

TES-389 is a spec for what used to be the DEX III stuff. ... It merely continues the existence of what was essentially DEX III. It also specifically address the seal compatibility issue. Any licensed TES-389 will not cause seal issues in older Allison trannies...

Right. TES-389 is not a new spec. It basically says fluids that were formerly licensed as DEXRON 3 AND pass a Viton seal compatiblity spec, meet TES-389.

The focus of TES-389 is prevention of hardening Viton seals. Otherwise, a fluid could meet the DEXRON 3 spec (including DEXRON 6) but contain additives harmful to seals.