Irregular idling
 

I have a 99 f250 with a v-8 triton
With irregular idle. It starts up great and runs great but after about 10 minutes of idiling truck almost stalls and then returns back to normal rpm. Also when I was just sitting in the driveway in park and reved up the motor it stay up almost like its stuck and slowly came back down. I checked the foot pedal to see if it was sticking. However it is moving freely as it should. Any one dealt with this?