98 Voyager- vehicle vibrates upon accleration

Hello all, great site!
Vehicle (98 Plymouth Grand Voyager, 3.3 engine, 160K)
I purchased a 1998 Plymouth Grand Voyager. Shortly after purchase the following were replaced for one reason or another, transmission (rebuilt), starter and engine. With the latest replacement of the engine made, I now experience a vehicular vibration or shuddering whenever I depress the accelerator anytime traveling over 40 miles and hour. Once my foot is released from the accelerator the vibration stops. I was also told by the mechanic that replaced the engine that there is a small hole in the exhaust pipe. Your suggestions will be greatly appreciated.