I have an issue with my 2001 Grand Prix, between 2,000 and 2,500 RPM (50-60MPH)the car tachometer begins to surge, or bounce up and down. If the car is given more gas the surging disappears, which eliminates a slipping transmission. Other than when presented with the above condition the car runs fine. This is more of an annoyance than anything, but do not want it to escalate into a high cost repair. Note:There is no malfunction indicator lights on the instrument cluster. Any help would be greatly appreciated.