I have a brake question on my 1990 Chevy K1500. It's my plow truck so this is some what of a tool question. Lately I've started having problems with my brakes. I'm not loosing any brake fluid, so that should rule out leak. When I start out I have good pedal pressure and height. A little push on the pedal and the brakes seems to engage. As I plow, usually about an hour or so, with a lot of starting and stopping, due to the way my driveway is, I seem to loose pedal pressure as the pedal does seem to apply the brakes until close to the floor. I can always stop though. I'm at a loss as to there the problem is. Might add the truck does have power brakes.