Yes, I cleaned the area where the IAC extends into to cut off airflow. there wasn't a ton of carbon buildup in that area. Good suggestion though, I missed that area the first time I had the TB off to clean when I first got the truck.

 

So the new Mopar IAC and TPS arrived today. I have installed them and they yielded no different result. With the vehicle speed above ~5mph, the engine will not return to idle from above 1500 RPM. With the vehicle sitting stationary, the engine can rev well past 1500 and return to idle no issue. I'm just not sure how vehicle speed is related. Just to test, I unplugged the speed sensor on the rear diff, and it ran fine. The engine rpm would drop regardless of vehicle speed when the clutch was pressed. Unfortunately without that sensor plugged in, no speedometer. Going to get a different speed sensor for the rear diff to test, but I'm not sold on it being the cause, as the speedometer works fine with the current sensor.

Not sure what else could be contributing to the issue. I do not see any other speed sensors on the transfer case or transmission.

*EDIT*
Just replaced the ABS speed sensor on the rear wheel. Same issue occurred.

 

Did you reset the pcm after installing the new sensors? If not it's not learning the new sensors. Resetting the pcm: Disconnecting the battery and draining the memory (leave it sit over night, touch the two leads together or turn the headlights on. Then drive it for a while and see what happens.

 

PCM was reset after sensors were installed. Battery was disconnected in the morning before the sensors arrived and I didn't install the sensors until later that night. It was unplugged for around 8 hours. When I plugged my scan tool into it, all the monitors were reset. I'll give it another go tonight after work, couldn't hurt things.

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The only thing I can think of remaining for it is an issue with the PCM itself. Trying to find one local to test against the one I have.

 

So I fixed it. Turned out to be the PCM all along. Bought a used one out of a 01 Ram 2500 with the 5.9 and a manual, somehow that seems to have fixed it. RPM now drops like a rock when the clutch is pressed in.

Thank y'all for your help along the way!