What should I use?

I know I could have searched but Im to stupid and lazy to do it.

The OE stuff is fine. I'm using a mix of OE, and Redline about 5 quarts. I didn't notice any difference, and the OE fluid I drained out looked new.

Mercon/Dexron III or Nissan Matic D or whatevre the OE stuff is.

Like any fluid, the best fluid is fresh fluid that meets specifications.

That being said, the correct synthetic will perform better under a greater variance of operating conditions. I use M1.

If you don't mechanically exchange the fluid, then you are mixing with contaminated (degraded) fluid. A ATF cooler is a large benefit to extending the life of the fluid.

Same goes for the PS fluid. Not much volume, lots of stress, degrades quickly. Replace it at the same time with M1 or the synthetic of your choice that meets OEM specifications.

Won't matter too much to you (WI), but there was a thread where the guy measured tranny temps with old (unidentified) tranny fluid anmd M1 synth and saw a 10 degree decrease in operating temps. That and Mobile 1's reputation in the lubricant category is enough for me .