txab

Check compressor clutch for proper air gap. If not running lightly tap face of clutch, see if it engages.

I'd check wheel hub bearings

Does your pan look like this?
 

 
 
There is a shelf built into some pans (upper left corner) where the dipstick comes in. It is designed to stop the stick from going to deep. If this is the case you may have the wrong dipstick

Already got one.
 
http://www.gm-trucks.com/forums/forum/170-technology-devices-gaming/

I think there was a thread recently where the poster had a squeak and I believe they did track it down to being an internal problem. By all means check the AC belt, etc
 
 
 
 
http://www.gm-trucks.com/forums/topic/154474-2009-53-engine-sqeaking/?hl=%2Bengine+%2Bsqueaks&do=findComment&comment=1368591

After clicking "View New Content", look to the left column, "By Time Period". Choose away

Yes!

I think you got the AC numbers right. #'s on the right are Dorman. Rockauto does have all 3, you just need to pull up 624117 by the part #. If you go the Dorman route
 
15809058 624117
 
15773661 624116
 
15809053 624124
 
I've used the Dorman lines as well as the AC line. Both have held well