The truck has developed a vibration between 50 to 65 mph that only occurs when accelerating and maintaining that speed. The vibration stops entirely when coasting. Any ideas?

 

Most likely u-joints. Try to feel if they are loose, although I've seen them bad enough that the bearings are disintegrated and holding things tight so it feels as if nothing is wrong. But u-joints would be my guess.

 

U-joints was my thought as well, and I think you're right on with the frozen bearings holding things tight. Should be replaced anyway. They've lasted a long time at 180,000 miles. Thanks for the suggestion.

 

Yeah thats a really long time for u-joints to last. It would me my best guess.