1998 Ford Contour RPMs

The car runs smoothly up til speeds reach 55+ or so

sometimes (and only sometimes) then the RPMs will raise, and the car feels the way it does when it shifts hard, then the RPMs will drop back to normal

and once the car red lined randomly while I was on cruise control, so I hit the brake.

also, someone had suggested maybe it was my Overdrive, but I turned that off while I was driving today, and the car still performed poorly

i think this is a transmission problem, but im not positive