High Idle

I have a 2001 Dodge Durango 4x2 4.7 V-8 with 54,000 miles on it. One day the truck just started to idle high after start up( about 1800 rpm) and would only come down if you rap the gas quickly like an old carbureted auto. After you rap the gas the idle will be normal for a while, but will return high once again during start and stop driving or when you turn the a/c on. If you rap the gas again several times the idle will return to normal again, but will eventually go high again. I had it at the dealer and several reputable shops and all report NO vacuum leaks and no codes stored in the computer. I have had the IAC replaced, the throttle body cleaned 2 times, an induction cleaning service, the fuel injectors flushed, the spark plugs replaced and the air filter replaced. The only thing that helped for a short period of time (several days) was the new IAC motor! Can someone PLEASE HELP?