I have a 1995 Chevy 1/2 ton with a 4" lift. I had the rear end rebuilt about 4 months ago. A real bad vibration occurs in the rear of the truck between 45 and 55. Also when I let off the gas abrutly going about 65 the driveshaft almost wants to bind up and the bolts on the u-joint are hitting the driveshaft. It is almost like the axle is moving and the angle of the drive line is changing. When the truck is just sitting the angle is fine also I replaced the u-bolts and u-joints but that did not take care of it. The truck has been lifted for 6 years and did not do this before the rear end was done. Is it possible they put something together wrong in the rear end when they did that or is it more likely that there is a problem with something like bad leafs or something. Thanks for any help.