It may be that the rubber center has come apart and the metal ears (designed to help you limp home) are doing their job. Another test would be to drive a fixed speed (say 30 mph in 3rd gear) and alternate a slight lift and then a slight push on the gas pedal. If you hear a clunk, then it's the rubber center clutch.
Another method (if you have the car on jack stands) is to try to rotate the torque tube drive shaft coupler (engine not running and trans in neutral, of course) to see it there is more than about 1 degree of rotation. If so, time for a clutch.
Here is a picture (stolen from another forum) showing the metal tabs involved:
