Reman transfer case? That can't really be called a 'GM truck' problem.
If the instrument cluster fails you, get someone who can solder to replace the stepper motors (if you're having gauge issues). My dad's '04 had an intermittent complete loss of the whole cluster power. Despite sending it to a place that reworks them, it still flaked out. I reflowed the solder on the main connector to the circuit board and cured it. Just a little time and no money.
This guy claims the 'service 4x4' message is from the switch panel and shows you how to test it:
https://www.youtube.com/watch?v=JNWxhIWs8Uk