I have a 96 Chevy S-10 pickup with 105k miles on it. It is a 4 cylinder, 2.2L with a standard transmission. In the last year I have had a new alternator, battery (associated cables), catalytic converter. muffler and most the AC system installed.

A new problem has come up. At highway speeds (67-71mph) the truck vibrates loudly. This only happens at this speed, and occurs whether I am accelerating or coasting, with or without the AC.

Anybody have any ideas?