GT out of balance?

[SpeedJunkie]

I have a '95 GT, stock engine, 5 speed 138k miles and I am running out of ideas for this problem: there seems to be something out of balance (or at least it feels like it) when the engine revs between idle and 1000 rpm and under wide open throttle past 4200 rpm. It is a large vibration that rattles the stick shift and the body of the car with force.

The engine does not miss or exhibit any other mulfunction and runs strong, but it feels as if something is going to fly out of the engine compartment or underneath the car at any second. The vibration is evident when the car is not in gear (neutral) or moving, so I am thinking that the drive train is not the issue...

I have checked the vacuum lines for leaks (none found), replaced the distributor housing, replaced the spark plug wires with Ford Racing parts and switched to a MSD coil - no change.

Your expert opinion is appreciated before something does fly out or I toss the engine in the river... HELP and thanks!