03 Suburban electrical issue(s?)

My 03 Suburban has been pretty fantastic for years of service.  Over the past few months it has started to drain its battery when sitting, even with a new battery and an alternator that works fine.   As a result, yesterday it wouldn't start, so I put a battery charger on it.  Once it got enough charge in the battery the truck would start but now a bunch of features no longer work.  Things that don't work include the interior lights, radio amp, power windows/locks, the 4WD button lights, the 4 gauges on the right of the cluster, and probably more.  The gauge cluster also has the ABS and airbag lights on said "unknown driver", even after I've tried several key cycles in the door and ignition.   

So it seems that there are a few questions here, but as we have so many GM truck owners I figure someone else has run into this. 

First, what is causing the parasitic drain?  I know I should use an ammeter and pull fuses but I understand that there are some common issues on these for this problem, like the gauge cluster (which has been a bit wonky for about a year now) and potentially the auto climate control and the steering wheel control sensor (this one has Quadrasteer).  My in laws also have an 04 Suburban that also has battery drain issues and is equipped basically the same (no QS).  Anyone had parasitic drain issues with their GMT800?

Second is what is my current problem?  It only started once I charged the battery, so I'm assuming there was some sort of power spike when doing so.  I have checked all the big fuses and everything is fine, and as it impacts so many areas I'm thinking it has to be some larger system.  An internet hole lead me to potential issues with the class 2 data link, or BCM, or ignition switch.   I'd rather not just throw parts at it, has anyone encountered a similar issue?  
 

As this just happened last night and I had things to do I didn't dig in more.  I have the battery disconnected from the car and charging now so hooking it back up with the charged battery and hard reset on the car are the first thing I'll try.  

Well, the deep charge and hard reset worked, everything is back to normal.  
 

I still need to figure out the parasitic draw though.  What's odd is that the in laws Suburban does the same thing, which makes me think it is a common problem.  

Friend of mine has a 99 Suburban. If it sat for "too long" the charge would drain. It came from the courtesy lights/switch. He has left the fuse out.

Most modern vehicles will drain the battery if they sit long enough. The 2000 Dakota I had said in the manual to pull the main fuse if it was to be sitting for more than 20 days.

Put a solar charger on the dash, it can keep the battery up while sitting.