2001 F150 Screw. Truck recently started vibrating badly when starting off. Vibration goes away at my normal speed, 110kph (70 mph). When I start to slow down the the vibration comes back, Had the wheels rotated, no change, had them computer balanced no chance. I'd take it to a tire shop, but I don't have much faith in their skills, small town. Any ideas? As usual thanks for any help.

 

umm the u joints in the drive shaft need replacing?...that's my only guess