i just changed the rear end, tranny and motor with Royal Purple, and i must say, out of every bolt on i have, this simple mod(if you will) made the BIGGEST seat of the pants difference. its like i was driving a new car again, it felt like the first time i took her for a test drive, like i had gained some power back from years of crap fluid changes by previous owner.
used the Synchrotech or whatever(the manual transmission formula, not the ATF Formula) for the tranny. used 85w140 for the rear end(it was either that, or 75w90). used 5w30 for the motor.
my rear end under-2-mph moan is still present, but after getting up to normal operating temps, burnouts, lots of WOT runs(loving the new feel), it made a slight whine at takeoff, nothing like the immense moan it had a day ago at the track(you should hear the vid of me staging, the car moaned like i was trying to move her with all 4 locked up). hopefully this will either wear into the rear end and maybe even get rid of the moan after a few miles, or save me some time while i gather funds for a 31 spline eaton built rear.
now to the tranny. it now shifts like a Tremec 3650 SHOULDNT. its purely efforless and notchless. i feel almost desensitized from it, but thankfully the sound of the shifter hitting the bumpstops with a clank lets me know im there. but dam, its effortless. from 2nd to 3rd shifts, i merely have to feather my arm forward, and its like an act of devine inspiration moves it the rest of the way. i changed the fluid because on the way to the track, my tranny chatter came back(or maybe i just noticed it again), since it was gone after my last fluid change, so figured what the hell. now the chatter is gone, and driving is silencio from el drivetraino.
i am a believer in this stuff now. i used to think "eh, oil is oil" but not no more. on a hunch to alleviate my problems, i have seen the light.