Engine rpm fluctuates while crusing

What is your question?

My auto idles, accelerates, and shifts smoothly, however, the engine rpm fluctuates while crusing. The tac will drop 200 - 500 rpm momentarily then return to its original speed. This appears to happen randomly and can occur several times a minute and at any speed. The OBD does not throw a code. So far, I have changed the air filter, cleaned the MAF sensor, and ran through a tank of gas laced with Sea Foam. Any suggestions?