RPM'S OUT OF CONTROL

I have a 2002 Dodge Ram 4.7L with Hwy 118,000 miles. All the maintenance is done. The rpm's seem to have a mind of their own, they continue to rev on their own from 1800 to 3000 rpm (They usually go in 200 to 500 rpm intervals) when I reach speed (above 50 mph). It will also do this with the cruise control on. If I stick my foot into it and accelerate fast, it will typically stop for about ten minutes give or take a few. It shows no codes on the scanner, and no check engine light. One shop said it was a vacuum leak ($ fixed $), worked for a while; other said it was dirty throttle body ($ cleaned $), again worked for a while. All this did not work to solve problem. Are we looking in the right place? Any other suggestions would be greatly appreciated.

Thanks for your time and effort on this matter.
Pedro Guerrero III