I live in TX and I just bought a 1997 F150 4x4 from NJ. When driving 60 mph on the highway, every time I tried to push the gas to accelerate, the truck would shake almost as if the rear brakes were grabbing on to the back tires. I took it to a friends shop and he said that the brakes and U Joints were still great but thinks it may be rust in the rear end??? He hooked it up and had it goin 90mph and said nothing was grabbing at all. Any help is appreciated. Thanks guys.