I have replaced both the encoder motor and the actuator. still same problem on 2003 Chevrolet Avalanche 2500

I have taken the time to check the grounding the fluid and the connections. It still will not shift into 4 wheel drive. If I stop and put it in nutural I can get the 4 low to engage but the 2 wheel light up as well. very loude shift but I am not confident that it is really engaged.
also can not get the transfer case to register nutural on the selector.

Asked by for the 2003 Chevrolet Avalanche 2500