Hyundai Repair: Changing RPMs, hyundai accent, voltage spikes

Question
Daughter has an 03 Hyundai Accent. Problem started when at highway speed for sometime(3 hours) the rpm's would shoot up by about 300-500 for a couple of seconds and then back come back down. The more you drove it, the more frequent this would happen, until it would do it about every 20 seconds. As time has gone on, it takes less and less time at speed for this to occur. No codes are being thrown or stored. My guess is the TPS.......what do you think? Two shops have not been willing to swap anything out because no codes are thrown. Very aggravating and want to get solved before out of warranty. I can only think of TPS or perhaps the MAF. Anybody else have this problem?

Answer
The TPS is right on mark.  A common problem with the TPS (although not on 2003 models) is that intermittently the signal voltage spikes up, making the ECM think the throttle is opened.  This will cause odd rpm variations, high idle, and erratic automatic transmission shifting.