I have a 2000 Bonneville SSEI with 60,000 miles and I am experiencing a engine surging issue. While on cruise control at 60MPH everything is fine untill you start up a mild to moderate grade and the RPM's start surging from 2000 to 1500 back and fourth and the vehicle starts bucking but if yuo take the car out of drive into third the problem stops with the higher RPM's. This vehicle has recieved a new fuel pump, TPS, and new coil packs as one was corroded and I recently changed plugs and wires. Any Ideas? Help please.