Battery going dead

II have seen posts about Trailblazer batteries going dead. I have just started having that problem with my '03. I have a 3 mo old battery, posts clean and if I don't drive it for 2 or 3 days it goes completely dead.
Yesterday I had the battery checked by auto zone where I purchased it, and the battery tested good and alternator was charging fine. Since the battery was in warranty, I had them replace it and I went to a HD battery.
Now my question for those that have had this problem, is there something that could be draining the battery overnight. Everything is off, key out. I did have the dash pulled to change the actuator cam two weeks ago.
I remember reading how to test to find out if there is an open circuit, but forgot what it was.

My 03 did the same thing this past weekend. Battery checks good. I smell the computer. It is supposed to turn things off as rundown protection but maybe it is not happening like it is supposed to.

Has anyone seen a solution on this ? - my 2004 just started doing the same thing... with two years left on a 6 year battery and battery and alternator tested ok:banghead: