I have a weird brake problem that just started on my K5. First of all, I haven't had any time to look at it further but I was hoping to get some helpful leads as to where to start. This weekend I had it on the hoist at work (which I use all of the time) grooving my tires. When I went to pull the truck out the red "brake" light came on and the pedal felt slightly "weird", but didn't go to the floor or feel overly mushy. Everything was fine when I pulled it into the garage. I went out on the snow and ice covered parking lot and tried the brakes out......the fronts easily locked up but the rears did not, even on ice, so there is little or no braking on the rear. The brake light stays on constantly. The fluid level in the reservoir is fine and I did not see any obvious external fluid leaks. It's an '90 K5, 60/14FF, rear discs........I've been running the same setup for several years with no issues. Any thoughts?