Ive got an early 90's GMC Topkick 366 gas 5 speed manual. The driver side rear brake caliper keeps trying to stick. The Axle Hub gets warm on that side as well. The truck has had new rear calipers, hoses, brake pads. The only thing that has Not been changed is the rubber brake line that comes from the metal line on the frame and divides the fluid to each side on rear axle. What could be causing this issue? Also the brake pedal will get hard to push when the sticking occurs. The mechanic that worked on truck now has the electric brake motor (truck has the famous hydro-boost system) wired to run every time the pedal is pressed even with engine running. Any ideas would be appreciated.