02 with a 3650. ive gone through whatever red fluid that was in it when i got it, to store brand mercon v, to mobil 1, to pennzoil synchromesh. I dont remember any details about the original fluid. but after doing some research, i was nervous about the store brand fluid, so i grabbed mobil 1 thinking it would be nice and good quality. winter month shifting sucked until it warmed up. and no matter what, ever since i got the car, 5th gear would make a grindy rattly noise. I found with the mobil 1, that if i add a little fluid (no more than 3.7 quarts total) It minimizes the noises from 5th gear. i think right now, i have a little over 3.2 quarts of synchromesh in it. I want to do one more change in the near future though, mostly to cycle out the remnants of the old fluid, and make sure i get as close to 3.2 quarts of fluid as i can. synchromesh shifts best in any (florida) temperature. Cant vouch for snow weather.
Oh and the rattling noise goes away after the transmission has warmed up. i used to have an audio recording of the noise, but it sounded WAY worse and alarming in the audio recording that it did in person. My best solution so far is to try to stick with 4th gear and below until i ran the gears long enough to warm up, then speed up and cruise 5th.
2002 GT 5sp. 16x,xxx miles
Steeda Exhaust, C&L plenum, BBK Throttle Body, Steeda Underdrive, Steeda short throw, unknown stage clutch. Rear main leak. Compressor seal leak. Steeda lower control arms. good tires.