Electrical gremlins, flashing security light, fixed..
 

In the last year I have been chasing electrical gremlins that even the Chevrolet dealer could not find or fix. I was starting to get quite discouraged. I decided to pull the negative cable from the battery, follow the cable to the engine block and check that connection. I took the bolt out (I used a 1/2 inch wobble head but, I think it's a 12mm). I used a wire brush to clean the block and then cleaned the bolt on the wire wheel. It's been three weeks and not one electrical issue. Fingers crossed that it's fixed. The security light coming on while driving was making me real nervous. If you have any weird electrical, intermittent issues, try cleaning that connection on the block. You get to it from the top. On a 4x4 there's no way to get to it under the truck.