i got a 01 sixxer auto i put 4.10s about 3 months ago, then i tried to mod my tranny and i messed it up so i got one from the junk yard, after the install i later realized that when i would go about 75 mph and let go of the gas the car would vibrate then stop then vibrate again until i reached a certain lower speed, now its doing it more and more often even at lower speeds like 30 mph i took it to a shop today and i was told that my driveline was crooked so i got another used one but it still does the same thing but just a little less, what do u guys think?? bad gear install?? or bad tranny? the gears do whine alot aswell and i do kinda notice that when im on the free way and let go of the gas the gears whine and after they stop the vibration occurs.... maybe it can be the transmission mount what you guys think?? please help

 

Take it back to whoever did the gears and have them correct it.