In the 3650 in my '02 GT it's felt the best on either Mobil 1 ATF or Royal Purple Synchromax. I will say though that in normal everyday driving they both feel the same. But when really getting on it the higher RPM shifts feel a tad bit smoother with the Synchromax.
Also, if you haven't already, drop the amount you put in the trans. That was the main thing that Tremec was very consistent on to address the notchy 1-2 shift that would grind a little. Put in 3.2 qt's instead of 4.
Also, if you haven't already, drop the amount you put in the trans. That was the main thing that Tremec was very consistent on to address the notchy 1-2 shift that would grind a little. Put in 3.2 qt's instead of 4.