trans oil

Ford TSB

For a quick answer, Ford has a TSB that authorizes Mecron V to be used in power steering pumps and manual transmission for all applications that used to call for Mecron IV.

Dexron III can be used. But have you tried to find any lately?

I am sure others my chime in about Royal Purple, Mobil, or Pennzoil synchromesh products. I do not have any direct experience to know if one is better than the other.

Tremec released a service bulletin about fluid recommendations (can't find it now). I believe the bulletin recommended against synthetic fluids. Something about the different metals and each needing different trace additives.

Tremec Service topics number 3-02
http://www.mach1registry.com/images/TREMECServiceTopic3-02.pdf