I'm new to this forum....first post in fact. I just (minutes ago) diagnosed my truck doing the samne thing, with the batteries being run down over night. I had a draw on the batteries when the truck was turned off...bit of a hassle to figure out...but mine ended up being the instrument cluster drawing power when the ignition was off.
I pulled the fuse for the instument cluster and am on here right now trying to figure out the fix for this.
To diagnose of the truck has a draw, What I did was completely disconnected the driver side battery and only the neg. on the passenger side. I then ran a test light from the battery post to the terminal snd sure as sh*t, the light came on. Make sure that you have the doors closed (interior light off) and unplug the light on the underside of the hood so these dont fool you to think they are a draw. I then went in and stared pulling fuses (one at a time) until the test light went out. In my case, it ended up being the 10A fuse for the instrument cluster. Hope that helps.