Battery Draw in today's vehicles especially Light GM trucks is pretty common. The ECU is active and so is On-Star as well as parasytic drains like headlight run-on, etc. 1999 - current production use a pretty small battery to begin with. Mine died 2 days after the 36 month prorata warranty ran out. I decided to do something about it bought a battery back-up system from ATC-Guardiansys.com. It was easier to create a defense by giving nyself an extra battery that is isolated from everything until I decide when to use it. Works gret and allows me to add auxillairy equipment without worrying about my starting battery any more. 300.00 later I don;t worry about it any more.
http://www.atct-guardiansys.com/
dbrakeman