New battery on Truck died quickly

[penguinwise]

Hey all. I have a random question to ask everyone. I have a 72' GMC 3/4 long step that seems to be having some electrical issues. Two weeks ago when I went to start my truck, the battery was dead. This was after I had been driving it several times a week so I was a little puzzled why the battery would be dead then. I figured as the battery came with the truck when I bought it over a year ago, I mideswell just replace it as it was most likely at fault. So I purchased a new battery, hooked it up, and the truck started right up and ran great. The next day I went out to make a run to the hardware store in the truck, and it would not start. Battery did not have Any juice to it. I chalked this up to it possibly sitting on the shelf at the store for awhile. I put the battery on a charger all afternoon until it read full, put it back in the truck and started it up without a hiccup. Then, two days later I needed to move the truck, went out to start it again, and sure enough it was completely dead.

I obviously have a pretty major power drain going on somewhere. Anybody have some suggestions on where I should start looking? First off I have checked the obvious places making sure everything in the interior was turned off, also double checked the no lights were staying on after the truck was turned off. Any suggestions on where to start would be most helpful.