I have a 1994 chevy s10 blazer 4.3, i had braking issues with this truck for the past 3 days, vehicle would be driving and as soon as it gets between 20 and 25 mph for some reason the brake would apply on their own and prevent the vehicle from gaining any more speed problem also includes an occasional screeching of the tires when the brakes apply on thier own, I replaced both front calipers,brake shoes, and wheel discs...WHAT CAN BE THE PROBLEM?? :? [/b]