[LS short box]

So this is a bit old school but about 40 years ago a battery drain was by sorted out by disconnecting the negative battery cable leaving the positive cable in place. Connect the 12 volt lead of your high tech, at the time test light to the negative battery cable and the battery terminal and pull fuses until the light went out. If it goes out you found the drain.
So having said that I did a LS swap in a 73 Camaro that all of a sudden I had a battery drain over about 2 days as you have said you have. Pulled all fuses and still a drain. Come to find out the clip on cover on the starter solenoid had rubbed thru the main battery cable making a small but bad short to ground. Could of been bad.