My A/C has never worked 100% correct. Right now its not blowing any air out of the vents for the second time. Before, it would not blow through the floor vents. Its been a real pain and makes for a hot ride.

Those amber cab lights need to be looked at if you have them, I've had four replaced so far. Mine were holding water.

 

I would listen for a howl from the rear dif. Lots of posts about this on various threads. Many dealers are denying it's anything wrong, and some can't even hear it! I had a new gear set put in at a dealer who has mechanics who can hear things that shouldn't be there, and are experts at their trade. My truck was bad from new, and was getting worse. After the fix it is great! Most of the trucks with this problem reported on this site seemed to be '03's with the 373's.