It was wiring on mine, I had frayed wires. I was told it was from underneath the vehicle. Can't find my paperwork but it was wires from either the encoder motor or the control module.
They way it sounds is that you have an electrical problem too and probably moved the wire enough while doing the t-case switch to get low to work. So I would say check all the wires to see if they have any bad spots.
Don't know how much money you have to work with but I took the easy way out and took it to a chevy dealer to get it fixed. $100 to "inspect it" but that cost goes towards fixing the problem. Only cost me $200 from them.