2002 Pontiac Sunfire at freeway speed, car jumps up a gear

Engine Performance problem
2002 Pontiac Sunfire Front Wheel Drive Automatic 175000 miles

at freeway speed the transmission seems to jump up a gear than back, and continues vairously while on the freeway. It also does this when im in town driving giving me the same problems. I changed fuel filter, plugs, wires, replaced a bad wire in the front wheel sensor, rear brake wheel cylinder and brakes they were so bad they had to be torched and beat off im not sure if that caused any damage or not but it seems fine. No other lights are on indacating any problems. I do all of my one repairs this one just has me stumped although I did take it in for the rear brakes.