abnormal idle

[880lbs feet torque]

i have a 99 psd build date 02/98. i have had the tranny rebuild 4 times in a year and on the 2nd time it was rebuild, once i get off the high way or after i goose it a little the truck stays at 900rpm. it use to go away when i put it in neutral and now when its put in neutral it jumps to 1000-1500. i have to put it in park and then it goess away. i have no idea what it could be. i recently replaced the app sensor( accelerator pedal position sensor) and it was off by 1.5 volts at wot. every shop around here tells me it not a big deal, but it is. also i dont know if this ties in with it but i installed guages the other week to watch everything and at 10 lbs the guage flutters and the more boost the worse it gets. please help. everyone here either wants a million bucks for advise or they have no clue what they are doing. thanks

[ProStarPony]

your ICP sensor could be going out of wack, that sensor is one of the main contributors of idle quality and performance. Have it checked or unplug it and see if it is internally leaking oil, which will throw it off as well...

[880lbs feet torque]

what exactly is the icp sensor and where would this be located so i can check it please?

[Mikesf250]

It is located in the valley just below the valve cover on the drivers side toward the front. there is a thread here somewhere showing sensor locations.