When i have my a/c on my truck idles down real low and idles back up, but it does it constently like it wants to die. It kinda sound cool but it shakes the hell out of my truck. Some times it does it when the a/c is not on. Any Thoughts? 02 2500 5speed SO

 

Sounds like your alternator is not doing the job. I Had same problem in my 97. It started out as doing it a little here and there specialy after short trips here and there. I could be wrong. If you want you can check by disconnecting the battery cable's and put a volt meter on the cables coming from the alternator.
Check your pulley wheel from the AC as well , see if it runs free, it might be seazing up.

Good luck

Mike