I recently purchased a 1993 F-250 Ex. cab long bed, 5spd with the factory turbo'ed 7.3. I knew when a I bought it that the U Joints were bad, as I could hear them clank when I put the truck in reverse. Just today it started shuddering (not the best at to describe it) in 2nd and 3rd gear. The engine idles smooth and it doesn't sound as if it's missing. It also doesn't happen at higher speeds in higher gears. Any idea what might be causing that? It has 315k on the engine, per the odo, and supposedly 15k on a rebuilt trans, though he didn't have any paper work to prove it.