I'm trying to troubleshoot a high idle issue (when the engine is warmed up).

*TPS adjusted correctly
*Fresh coolant, new thermostat, air bubbles have been burped from system.
*All vacuume lines are routed correctly and in good shape
*AFM has not been touched*
*Idle mixture screen turn the entire way in
*Not throwing any codes

With the idle screw in the entire way it idles around 1500 RPM's.

Here's the kicker, I took the truck out wheeling last weekend and it idled where it should the entire trip (in fact, i had to turn the idle screw back up where it was previously). It would only idle fine while crawling / staying at slow speeds, which was over 5 hours this day. About 5 minutes after I hit the paved roads I pulled in into neutral and it was idling at 1500 again.

I'm thinking it's sensor related; the coolant temperature sensor acutally. Since this is an uncommon thing to fail I thought I'd get some feedback before I pick one of these up.