While driving the transmission dropped out and vehicle rolled to a stop. on 2005 Chevrolet Suburban 2500

The suburban would not move when the 2WD button was engaged. After cycling through the other button options, I was able to engage the transmission when the Auto button was lit. With the suburban in park, I engaged the 2WD button and the suburban began to roll as if the selector was in the neutral. How I solve this problem??

Asked by for the 2005 Chevrolet Suburban 2500