I have a 2000 Ford F-150 XLT supercab. When I am driving at a normal rate of speed the transmission seems to feel like I am driving over a bump in the road and it is comming from the rear end.This happens at 45mph and 55mph. If I go faster it seems not to be as noticable. There is 80,000 miles on it and the transmission fluid and filter was changed at 30,000 and 60,000 miles. This has been happening for at least 4 months. Any help is really appreciated.Thank You Deno