allright heres the deal., i bought a used rearend with a 373 gear and put it in today., i had the cover off and it looked fine inside., filled it and installed it today., i whent from a 273 to the 373., very happy with the pulling power., feels perfect untill im well into the rmps in the higher gears., 1st- 6000,,2nd 6000, 3rd 5500, at 5500 in 3rd it starts, as soon as i shift into 4th under full power its shaking, and same into 5th., really jaring feeling in the shifter., you feel nothing anywhere else or hear anything.,if i drive it normal it feels fine.,very smooth, ive drivin it a few times across gandy today., i have no idea how fast im going with the new gears., i feel nothing in between the gears.,i looked at the ujoint and it looked fine, i havent had the car long at all and really have pushed it up on top end., between being a covertable,welds and old brakes ive really never pushed it up high., i had a old factory clutch in up untill a couple of weeks ago and it was slipping up high when stressed.,so i really hadnt pushed it other that down low......what do you guys think?