2003 Chevrolet S-10 Shifting problem

I have an 03' Chevy Duramax/Allison. The shifting is not working properly. Sometimes you don't have D gear, you may only have 1 2 3 and R. Sometimes none work. Sometimes when you shift from R to D there is a loud bang noise. Sometimes the digital readout that shows which drive position your in, does not show, the letters and numbers are there just no line under the one your in. Part of the time you can turn the truck off and restart it and things will work properly for a short period.