Im a noob to the site, but far from it with trucks.. What worked for me was to pull the positive cable from the battery and hook up a ohm meter from ground to the open cable. Turn off everything, and close the doors, and the reading should show high resistance. (I use a non-digital meter) If there's a low resistance, start pulling fuses one at a time to see what circuit has the draw. My truck battery died also, and turned out to be that the radio drew too much from the battery (it was from the radio memory, even though it was off), but in my case the truck sat for a couple of months.