i got a question my rx7 vibrates on 3rd and 4th gear after like 3k and 4k rpm's no grinding tho. all the gears go in fine. when i put it in neutral it takes a min but then it stops vibrating. i checked my tires and tranny bolts and my ujoints on the drive shaft averythings good. i pulled the driveshaft and the yolk looked like it had wear on it and it looked like some of the metal on the yolk was ground off not by mutch tho. also when i pulled the drive shaft off there was any to none gear lube in the tranny. i kno that the tranny has to have at least 2qrts. 90wgear oil in it. i refilled it. what you guys could think its wrong? new seal for tail end tranny? new drive shaft? or new tranny? if anyone could help would b great. thanks for looking