blazer reving at 60 mph and up

I have a 96 Chevy Blazer 4x4 with 128,000 miles on it. the past couple of weeks I have noticed that at highway speeds the RPM's will go up and down really fast and I can feel it in the truck. It almost feels like someone is put their foot on and off the gas peddle really fast. Usually I take my foot off the gas and let it settle and it will go away for a little while. However today while I was starting to accelerate from a stop sign it started reving at just 30 mph. It isn't showing any codes. It has been getting hotter than usual. Fuel pump was replaced in 05, fuel line was replaced last yr, rear differential was also replaced last summer. Anyone have any ideas of what could be wrong??? Family and friends are telling me to junk the truck but I am not ready to give up on it yet.

How's your transmission fluid level? If it's good, maybe should have fluid and filter changed.

The only proper way to check this is to get a scanner on it while your driving and see what its doing. Other than that, your really just shooting in the dark. This could be a variety of things, from 02 sensor, TPS sensor, MAF sensor, could be fuel problem, EGR problem, could be a computer problem itself. A MAF sensor can cause erratic idling/surging problems, but so can the 02, EGR, and even TPS for that matter. TPS can be checked with a voltage meter, the EGR, you could unplug it and go for a drive and see what happens, the MAF well if you have no scanner, then its really almost implossible to check that one properly. This pretty much is the same deal for the 02 sensor.