i had bought some Castrol to change my spin-on with earlier, but i wanna drain the pain now, and put all new in, i planned on changing to Mobil Delvac synthetic ATF, buts its way higher, and i';ve heard about some atf's other then reccomended wearing out seals, so what Dex III should i use??? thanks

I run Mobil 1 synthetic Dex 3 working good for me.

If you're set on a DEX III product, you can choose the "conventional" stuff (not bad, but certainly leaves something to be desired). The Mobil 1 ATF (and similar products) are a much improved route; Mobil 1 ATF is a PAO based product, IIRC. Or you can go with a DEX III TES-295 licensed, or cloned, product.

Just bought a Mag Hytec trans pan not to long ago and used Royle purple ATF seems to work great haven't had any weird heating problems and I tow a 26FT Weekend Warrior every weekend in Nevada.

I put Valvoline DexIII in mine, Castrol should be good also.

If you're set on a DEX III product, you can choose the "conventional" stuff (not bad, but certainly leaves something to be desired). The Mobil 1 ATF (and similar products) are a much improved route; Mobil 1 ATF is a PAO based product, IIRC. Or you can go with a DEX III TES-295 licensed, or cloned, product.


i looked it the regular mobil 1 synthetic ATF at autozone the otherday, started to get it, but what about all this where people are sayin some fluids other then dexIII are hard on some of the seals???

I've not heard that issue at all. Most of the available fluids out there for GM products are DEX III based, including the often touted "Transynd" and all the other TES-295 licensed products, and the related clones.

Only DEX VI has an issue with seal compatibility with older Allison transmissions. At the top of this forum, and the Allison OEM forum, is a post from me with a link to the official Allison matinenance schedule and the serial number break for the use of DEX VI.

Your year of truck should be just fine with any of the multitudes of DEX III based products at any autoparts store. Mobil 1 ATF is a fine product and will work very well in your tranny, if that's the product you choose.