I agree with the worn engine mount to check it simply open hood and watch to see if engine shifts signifigantly when going from park to reverese or park to drive.a clunking noise or slight bumping feel when letting off gas at higher rpms will indicate this as well.other than that check tune up conditions

Any check engine lights? It could very well be a worn mount. The mounts on these cars tend to stretch and lose strength at high mileage