I have a 2002 Chevy Avalanche and never had any problems with it until now. I have a slow charging system draining at night. I have to use a jump box to start the truck, but once I have it started then it will start all day long. I replaced the battery and alternator. I used to have 14.1 volts, but now I am getting 13.7-13.9 volts. I checked all of the lights, switches and everything is turned off and still getting a slow charging leak over night some where. Help.

I'm no mechanic but did you add any accessories to the truck.
Lights GPS System Sound system etc etc.
An stereo amplifier that would not shut off with the deck cause it's shorted would kill that battery every night.
I myself had added a set of driving lights and one of my Relays I had installed Jammed and it would do the exact same thing.. all day no problems.. but overnight wont start..
If I remember correctly you disconnect the negative from the battery and connect a Test light from the battery to the disconnect lead.. if the light turns on theres a load on the system.
yes you need to disconnect the light of the hood or push down on the switch to leave it off.

Hope this helps took me 2 weeks to find my dumb relay issue.