Quote Originally Posted by TLSheff View Post
Most parts stores should still sell Dex3, in different brands. I know they should because the GM Dealership I work at still sells Dex3, but we order Mobil Dex/Mer 3 by the case.
You have to use a Mobil product because GM does not support, produce, or recommend to anyone that Dexron III fluid be used anymore. It is an old, unsupported, and obsolete product. In fact, they stopped licensing around the end of 2006. So any Dexron III fluid made after that date is unlicensed, uncontrolled, and not something I would want to use at all. Your best bet is to go with the newer and better in all aspects Dexron VI fluid. Definitely a better choice.

The highway RPMs thing when you let off is normal. Nothing wrong, and the only way to change that is with a tuner as far as I know.

I'm not sure about the speedo in neutral. If it was just a one time thing, I would do it again and see if it replicates. The only thing that I can think of is a failing CPS (crank postion sensor) but that doesn't seem right. See if you can do it again and confirm exactly what it does.