I have a 91 HB truck, and had the center bearing go out. So, I replaced the whole driveshaft from a junk yard, ran it 5,000 miles and the center bearing went out again. I had the center bearing replaced, checked all U-joints and it still vibrates from 35-45mph in 3rd, 4th, and 5th gears. So, it seems as though it may be something else, however prior to the whole problem it didn't vibrate. Any ideas???