93 lx w/ 88 or 89 5.0, 5 spd- the car runs great but at anything over 2000 rpm the car has a horrible vibration !!!!! any ideas or obvios things to check would be great . . .
Crazy...I had a similar situation with my 1990 Notch awhile back. I replaced the harmonic balancer, flywheel, replaced the spark plugs & wires (just in case). Nothing made any difference whatsoever. Finally, I decided to turn my attention to the driveshaft. First, I tried rephrasing the driveshaft (unbolting it / turning it one bolt hole position / bolting it back up). I did this through all possible configurations, and took it out after each change. Still, nothing got any better. Lastly, I decided to just replaced my driveshaft with an all aluminum lightweight one. FINALLY...we have a winner!! It's now as smooth as "budda." So, with that said, I'd highly recommend starting there before wasting a lot of time and money (like me) on everything else.
Note: Apparently the driveshafts for the fox body mustangs are a type of 2-piece drive shaft (there's an internal shaft assembly inside of the actual driveshaft). For whatever reason (blunt trauma force, etc) the internal shaft can shift and cause the entire driveshaft to become out of balance. Just an FYI.