Will not shift from 2nd to 3rd

My Tahoe won't shift past 2nd gear. I just replaced the transfer case

No sound comes from the radio when on; amp was replaced already. What’s odd is when the radio is shutoff after a minute or two the cd icon will just blink. Is the radio unit dead?

So while on deployment my little 35-year-old brother and his incredibly smart friends took my truck off roading, took out all the seats and put some black seats from a charger in my beige leather interior cutting all the harness links to the seats. After scabbing together 35 wires apiece to each seat, the truck won't start at all, I hooked up my autel box and it won't even read the truck not a single module. I am a mechanic and am stumped I haven't looked any further because I'm packing up to move from phoenix to New Mexico and have to drag the shit box with me now.. any thoughts my brothers

This error stays consistently on the obd tester but only affects the truck every so often where it will turn off the radio and the hvac and cluster will shut down. When it comes back it goes through an initialization of unlocking and locking the doors then the cluster comes back reading things like service 4x4 and service stability. Only happens about 5-10 times a year for the last 5 years. I just really need help finding the wiring diagrams for this. Thanks