do what cubpak says he had the same problem as you and fixed it also take a look at your throttle body on the inside see if you can clean it up a bit

 

Today I check for vac. leaks with no luck. I did learn this though. While it was idling in park I uplugged the tbi(new) and then I plugged it back in while it was running. As soon as I did that I could hear a sucking sound (iac adjusted and started to bypass?) and it would hold idle when I put it in gear the way it's suppose to. I ran it up and down the road and the idle worked perfect. I shut it off, started up again and couldn't hear the sucking sound and wouldn't hold idle. I could repeat the first step(unplug/plug in) and the sucking sound would start and it would hold idle. Would you recommend replacing the O2 sensor next? I'm not a mechanic and not to handy with codes and voltmeters.

 

i would look into the IAC and TBI ( i have no clue about any of that...im going to have to do some research)

because if playing with one of those fixed the problem its in that area most likely

 

the codes on your truck are easy to read if you can count
and i would replace the iac it helped my truck out alot when it was doing what yours did and yes the 02 sensor is a big part of your trouble