Truck keeps on cruising after letting off throttle.
 

Hello, Im hoping to get some help with a problem Ive been having with my pickup. Its a 97 gmc c1500 with the 5.7l and I believe the 4l60e (around 105k). Heres the deal... I seem to have automatic cruise control. I can be cruising at 35 or so, around 1800rpm, let off the fuel and the rpm/mph doesnt drop. Seems like if I have the room to let the truck go without breaking, the tranny will shift down and slow the truck. Otherwise, breaking will make the rpms drop. I dont think the throttle is sticking because in park or neutral the rpms drop like they should. Any help you guys could give would be greatly appreciated.