Hello I have a 2011 Silverado Crew Cab 4.8L. Last night I was headed home when the truck gave out on me. I pressed on the accelerator and nothing happened. I had to get a tow truck to get it home and as the guy was getting the truck down he told me to put it in neutral to back it off but the truck did not move back as if it was locked up. Pushing it forward it does move but trying to push it back it is locked up. Can anyone point me into the right direction as to where and what to check, thank you in advance.

 

One way to help determine if it is the differential or the front part of the driveline would be to take off one end of the driveshaft and see if the transfer case with everything in neutral will allow you to rotate the flange that the driveshaft connects to. If you can rotate that part, I would remove the cover from the rear differential or raise the back wheels off the ground and see if you can rotate the driveshaft flange.
I have seen where the retaining bolt backs out or shears that holds the block in place for the axles sometimes moves enough to prevent any movement of the gears in the differential..