i have a 99 ram 1500 5.9L automatic everything was great with the truck, then the trans went, i replaced the trans with a trans from a donor truck with 60,000. my truck has 156,000. before i took the trans out of the other truck i ran the truck and everything was PERFECT with that trans and ever since that day (a month ago) i have a nasty driveline shake. it starts around 25mph and goes on. it doesnt shake the truck at all, its def in the driveline somewhere, like the transfer case or rear shaft. at higher speeds my 4 wheel drive shifter goes nuts. it ONLY shakes when i am on the throttle. the second i get off the throttle at any speed......its smooth as can be again. and if i put it into neutral at any speed and rev it up....its smooth. its only when the driveshaft is under torque. the truck is an extended cab reg box. and it is lifted roughly 4 inches and on 35's. But this problem i doubt is lift related bc it was fine for months lifted. ??? U joint maybe ???