997 f150 engine surges...help!!!
 

In the last week I have put $500 int diagnosing my truck. It idles fine, a little high at first then drops down to about 1000 rpm. When i put it in reverse or park the idle drops to about 500 rpm. if I sit there with my foot on the brake it starts to run ruff then clear then ruff and so on. It is not steady misfire. When i'm driving it cruises fine but when I press the gas it starts to surge. Nevermind the take off I couldn't spin the bald tires on asphalt if I wanted to. I have replaced IAT sensor, TPS,spark plugs, fuel pump, fuel regulator valve, EGR vacuum regulator, DPFE and sprayed intake cleaner in the throttle body. AND I AM STILL HAVING THE SAME PROBLEM!!!!!!!!!! PLEASE HELP