Toyota Repair: Engine Revs up at 70mph, throttle position sensor, toyota 4runner

Question
I have a issue with my 94 Toyota 4runner, when it gets up in 5th gear over 70mph the engine revs up every few minutes. It sounds like it is going into overdrive, and this just started to happen. The RPM doesn't go up at all, which is strange.  It's at about 150,000 miles, changed oil, oil filter, plugs (those new bosh duel point plugs), it has new exhaust (glass pack), new clutch, distributer, fuel filter etc. It seem to start to happen when the weather got warmer. Is this a symptom of the o2 sensor? Or something else?

Answer
Hi Pete,
Make sure the cruise is off, if its off and still does it, disconnect the cruise, pull the fuse for it, then try it. If it still does it, respond back to me. The throttle position sensor (TPS) could be dirty. We'll go from there, please let me know.

Tim,
ToyDoc