I went from synthetic to 4 quarts of non-synthetic and id made my shifts a lot better. I tried running at 3.2 qts but the tranny sounded like it was going to grind itself to pieces.
Not too much smoother no...It is a little easier feeling,but I still get a little bump or chunk between 1-2 and 2-3...the good thing is that it only happens during normal low rpm cruising..at WOT it shifts great.
I did not use RP synchromax though..I had to go with the best I could find which was RP Synerlec..stuff still cost $8.50/quart.
I guess the 3.6 quarts will be ok then for now..I plan on doing the fluid change again at the next 1-2 oil changes and switching to GM Syncromesh(heard it is best)....I just did this now because the tranny si going to get a bigtime workout this weekend.