Patience during testing.. Other ways to test:

 

Again the truck is dead... Pulled OnStar, Radio, and Heater fan and the heater fan Resistor...
Dead Again,.. what next.

 

i remember on older GM vehicles the alternator would get stuck and pull current. maybe try checking the alternator for a parasitic draw. another thing on gm trucks that can cause a draw is the instrument cluster not going to sleep after a set amount of time like it is supposed to. i personally had an issue with a bad XM satellite radio factory GM module going bad and causing a drain.

 

I had an intermittent drain on my 03 and it was the electrical portion of the ignition switch, it would act as if the key was not all the way off and drain the battery overnight.

 

Thanks, decided to give in and taking it to a specialist to see if he can save it.... lol

 

Don't throw in the towel yet and waste money. Battery discharges

 

I took mine to a mechanic and all they did was hook up a multimeter to the battery and pull the fuses until they figured out what made the constant draw go away. That's what you need to do to figure it out, either by using another multimeter to test the fuses or by pulling the fuses 1 by 1. The reason I didn't figure it out myself is because the blower motor was a big fuse that couldn't be checked with a multimeter. I didn't want to just pull the fuses but that's what my mechanic was doing. Also sometimes you have to wait a few minutes after each fuse is pulled because it can wake up other computers or do something to trigger the voltage

 

I've seen that fear of pulling fuses all over the internet. Just think about it, same when you disconnect/replace your battery. Still the easy way to find.