A couple months ago my 2003 F150 started idling very rough and hesitating to accelerate after about 15-20 minutes of driving. It acted like it was going to stall and the AC started blowing warm air but it never actually stalled. The check engine light did come on. After letting it rest at home for the night it drove perfectly fine the next morning on the way to the dealer. I ended taking it in to the dealer a total of three times over the course of the month, spending $2500 and it is still doing exactly the same thing it was doing before I brought it in. In runs great when cold but once it warms up to temp it rides really rough at idle and while accelerating. The dealer replaced multiple coils, all spark plugs, fixed some vacuum leaks, did a full fuel and air induction cleaning and I still don't know what the problem could be. Any help with diagnosing the problem would be greatly appreciated. I don't trust the dealer to fix it anymore so I'm hoping to pinpoint the problem and fix it myself.