Well, there's a couple of things that I'd check before I spent the money.
What does Stan idle at when he's warmed up?
If you're at idle, no lights on, a/c off, foot off the brake, engine fully warmed up and you turn the a/c on, does the idle go down and stay down or does it idle back up after the a/c turns on? If the idle stays down, the IACV is not working correctly. If it idles up, then it's working correctly.
But if it doesn't idle up, then we still have some checks. You'll need to get in there and disconnect the brown connector to the IACV. Turn the key on and check for battery voltage on the yellow/black wire. If there's no battery voltage there, then there's another connector that needs to be checked for power. It's located on the passenger's side valve cover, near the front. It's the black connector, and you're still looking for battery voltage on the yellow and black wire there. If none, then check fuse 15 in the fuse box inside the cab (by your left knee). That fuse supplies the power for the IACV and the Throttle Position switch. So if it's blown, I'd think you'd have more codes and Stan would be driving bad.
If you have all the powers, and Stan doesn't idle up, then you'll need to also check the resistance at the IACV too. After disconnecting the two wire brown connector, test the continuity of the IACV itself. It should be about 10 ohms. If the resistance is more, then it's bad and needs replaced.
But, if Stan idles up with just the a/c being turned on, then I'd retighten the grounds on the engine. They're the two bolt on the intake manifold next to the main harness as it runs along the side. Just give them both a little grunt tight, nothing massive.
See what happens and we can go from there.