2005 GMC 1500 series

You have a short circuit or something is still on within the truck that's draining the battery overnite.

Sounds like excessive battery drain with everything off. Check for interior lites left on, glove box, under the hood, anywhere. Best time to check is in the dark. Check the actual amp draw, if too much, pull and replace fuses one at a time. When you pull the fuse on the faulty circuit, the excessive drain goes away.

Your charging system works ok?

Sounds like maybe your starter is sucking the battery down. Lights on would drain a battery, but not kill it completely. Recharge new batt, & leave positive cable off over night . When rehooking positive cable back up...does it spark ??? If not....you don't have any lights on. If it does spark....& you don't have any lights on.....you have a major short circuit somewhere.

Ford Man in Michigan

Let us know what you find.