battery keeps draining?

Sounds like you have a large parasitic draw. You can try some of these:

https://www.2carpros.com/articles/car-battery-dead-overnight

This video is on a Ford but the principles for finding the draw are the same:

https://www.youtube.com/watch?v=6xFo_oHFF48

Attached are some of the wiring diagrams showing the circuits from the fuses, also don't overlook things that may have been changed on the truck in the recent past, added lights, stereo, amps, alarms and other aftermarket items can be a cause as rapidly as the OEM parts. GM has had an issue of power drain through a bad component in the instrument panel but usually the draw isn't that fast.

now the vehicle won't start.