I have a 2006 Silverado Z71. I'm at my wits end trying to figure out this problem. The ABS and brake light comes on and it says service brake system on the dash. Right before this happens the headlights dim. After the warning lights come on the speedometer bounces all around and the truck won't shift past 2nd gear. Sometimes it doesn't do it and drives and shifts perfectly normal though. I've replaced both front wheel bearings with speed sensors. I've cleaned all the grounds I could find. I replaced the VSS. It's still having the same problem. I will be extremely grateful to anyone who can help me figure this out.

 

Apparently it's a common problem. Bad wiring harness to frame grounding point. Directly underneath where you sit.