It sounds like your throttle plate may still be hanging up. Have you tried lubing the external linkage assembly and maybe the 2 points on the inside where the throttle plate pivots? Make sure you have no springs on linkage that may be broken, not letting the plate to return fully. Also do the IAC test for giggles. I've bought bad parts before. Check the condition of all your vacuum lines. You may want to do the throttle cable mod too if you have a lot of slack. Also, with the tube off the front of the throttle plate, look inside as you manually operate the throttle. Open all the way and let it return slowly as if letting off the gas. Does it hang up before fully closing? You may also want to check the TPS voltage.

 

 

I'm not sure of all the ways to test an IAC off the top of my head, but one particular way would be, the next time it sticks at 2000 rpm would be to unplug it and see if theres a change in idle. Do a search on the IAC and it will give you a great amount on it's function and malfunction symptoms. You didn't mention how long you have had this problem. Did you clean the ports where the IAC attaches? If your truck has anything not up to par, it can cause different symptoms. Like cracked or plugged vacuum lines, other sensors giving incorrect readings, things disconnected etc... Have you attempted to see if there are any pending codes in the OBDII?