I have a 2003 Sierra 1500 4WD, 4.8L, 4L60. I've only had the truck a couple of weeks, and I've been chasing an APP code (Acellerator Pedal Position). I replaced the accelerator pedal assembly, but the code came back so I decided to try cleaning the major grounds under the hood. So I disconnected the negative terminal, and then got under the vehicle and disconnected the ground cable from the motor. I cleaned the block and cable treminals, and fastener, and put it all back together. Now it won't start. Turns over, lights work, but no start. I pulled 1 of the plug wires and cranked it over, and it doesn't seem to have a spark. Any ideas what I did? Do I need to go through the computer re-set procedure? I've had nothing loose except the ground cables.