Surging RPM's

99 GTP. 118000 miles. When cruising at any consistant speeds and gently accelerate, RPM's will jump up about 1000 rpm's and jump back down. So it is like you floor it then let off, floor it then let off... But if you apply alittle more pedal it will stop. If you set cruise it will not happen either. New plugs and wires. I'm thinking a vaccum line but have no idea. Very difficult to do any driving. Thanks for the help.

Welcome to AF!

Sounds like the TPS to me if it's happening at any speed. Does it do the same thing when idling?

Idling and accelerating is great. It is only when at a steady speed and slightly accelerate. If accelerating alittle heavier it goes away.