Nightmare
 

2009 H-3------ Starts / runs fine, the issue is after starting if you don't put in drive quickly the shifter will lock in Park. Also wipers, auto setting lights go out. Radio works.

All the dash indicator lights, battery, TPM, etc, flash.

It will eventually correct itself and all is good, usually a few minutes but it has lasted 30 minutes.

Any ideas?

Sunroof? Is the passenger side carpet wet under the mat?

Welcome to HF.

That means 99% sure that your PCM got wet = electrical Gremlins.

Fix the problem before getting a new BCM.
https://www.hummerforums.com/forum/h...n-tubes-28548/

Vids: https://www.google.com/search?q=humm...bih=1069&dpr=1

Do you still have the OEM POS Battery Terminal Connectors?