Please Help

[Coal Burner]

I have a 99 F250 XLT 4x4 When driving between 35mph/55mph and maintaining speeds in that range my trucks shimmies and shakes like crazy. But if I take the truck out of OD or punch the gas it smooths out, untill the OD kicks back in. And it only does this between the above speeds, and when I try to maintain that speed, ie 50mph zone. PLEASE HELP ME.

[SmokeyWren]

Speed-related vibrations are almost always caused by something being out of round or out of balance. But it could be anything from driveshaft, U-joints, brake rotors, parking brake shoes, torque converter, rear axle, wheel bearings to transmission.

Good luck with finding the problem.