service 4wd

I got in my truck after work the other day and had all sorts of things light up. ABS and Brake lights are on. Service 4WD and Service Brake System messages. Radio on but no sound. 4WD selector switch does not work and showing in Neutral. (But it is not in neutral) The display for P N D...

I have an 03 Yukon XL 2500 with a 6.0 4speed. I am having the code for Service 4wd appear on my info center. I have replaced my switch and accuator replaced too. What else is there to replace so I can get my 4wd working again?