i personally used the GM synchromesh,but others on this site has used Pennzoil® Synchromesh,royal purple and amsoil....i recommend the GM synchromesh just costs $30 alot of money, but the tranny costs up to $2000.....
i know tremec recommends the synchromesh but im looking at buying a 3550 with under 1200 miles but the guy that has it said he ran motorcraft fluid while he had it but no track time. how much damage could he have done and is it worth takin the risk?
i got in touch with tremec and they said dexron III atf and mobil 1 atf are both compatible with the 3550 and the new tko 500/600 in case anyone else was wondering