I have a 2004 GMC Tahoe . I only drive it occasionally maybe 2 times in a week . Sometimes when I use the Tahoe after sitting , the battery is dead or too low to start it . I put a new battery in and it still drains it . I can't find anything left on . I also had the alternator checked and it was okay . Any ideas where else to look ?

Do you know how to do a parasitic draw test? YouTube is your friend.....

Ill give it a try . Thank you

Is there any aftermarket anything installed on this GMC Tahoe?

No aftermarket but I noticed last night that when I shut the engine off and get out , the radio was still on . I waited several minutes thinking it was on a delay . it stayed on until I opened the door again .

That is retained accessory power....if the radio is on, and you turn the key to off, the radio will stay on....as soon as you open the door, RAP goes off, and so does the radio.......if you don't open a door and sit there, it will go off in a preset time limit by itself...

I think this interval is 20 minutes.