I used the synchromax and purchased at americanmuscle.com. Most people are running it as opposed to the ATF. The synchromax is supposed to be made with the materials on the synchros in the manual in mind. RP lists it as a replacement when Mercon(V) is called for. I have read some guys using the ATF though.

 

Well I used RP Syncromax and it sure cooled my shifter down by 50% also it shifts easier. Had it changed at 65k and feels great

 

I don't think it's going to cool your shifter handle down when it's separated from the trans by a piece of linkage. It's more likely a case of heat transfer from the engine, cooling and exhaust systems on hot days that heat the shifter handle up even at highway speeds. These cars have a tall driveline tunnel that probably traps heat really well also when idling.

 

It definitely made the difference from a noticeably warm handle after cruising at 55+ speeds. This was with the Hurst billet shifter. I never noticed it with the stock shifter. Id say the tighter aluminum/poly mounts construction was transferring heat from the engine and transmission. After the RP went in it was noticeably cooler.