Four-wheel drive not working?

Truck is in 2wd now, but
Sometimes my truck would make me use the 4x4 selector switch several times to get it to engage. It would flash between the two options, the one I was on and the one I selected.
Often rolling a few feet would fix this.

After using 4x4 I couldn't get it to disengage for a while. Trying the button many times, turning vehicle off and moving it over n over. Eventually only the rear was spinning, but the service 4x4 light is still on, there was no sign it actually disengaged though.

and now no lights come onto my selector switch except when the keys in the on position " not running " No lights come on my selector switch for 4x4 except when I first turn the key.

Have checked both inside and out 4x4 fuses, Trac I believe it was blown but made no difference when replaced.

So, I've replaced the switch. Checked some fuses. Verified the switch is getting power, and yet my switch doesn't light up or activate any buttons.

There was a small ground underneath the truck mounted to the frame people online said to check. Cleaned that made no difference.

Can't get it to cycle through auto, 2h 4l or 4h.

Another weird thing is I've lost some kind of communication with the OBD port.

My check engine light is no longer on while running, and I know it won't go away without replacing a handful of sensors.

When Obd tool scans truck I'm getting 0 codes every time. Which is impossible.

I've replaced the 4x4 switch on the dash it made no differences. Please help! 2003 GMC Sierra 1500hd 4x4 6.0l gas, automatic.