1996 Jeep Cherokee thump on acceleration and deceleration

1996 Jeep Cherokee mileage: 62,000. I am experiencing 'bump' on acceleration and deceleration. It feels like a badly worn U-joint or excess play in differential. Upon the advice of Jeep dealership, I lubricated rear drive shaft slip yoke, no improvement. I had the differential inspected by a transmission shop and I was told actual gear lash =.010", spec =.008" to.012". I had the drive shaft checked for balance it was okay. I had rear the drive shaft slip yoke checked for wear and it was okay. I had the rear drive shaft U-joints checked and it was. I had the transfer case pulled and inspected by transmission shop and they replaced questionable bearing on main shaft. The problem was gone for a week, but then it came back. I had test drives performed by three transmission shops and they all said the transmission is okay. I had the brakes checked by two brake shops and of them both said the brakes were adjusted and working properly. Three mechanics indicated a problem due to axle 'spin', advised new shocks. I replaced shocks and no improvement. I test drove another 1996 Cherokee at the dealership and it had the same problem, but much less pronounced. Is this typical of later model Cherokees? I have driven a 1990 Cherokee for 160,000 miles and a 1988 Comanche for 50,000 miles, both 4.0L, auto, 4WD and I never experienced anything like this with either vehicle. Any ideas on how to rectify?