1992 Chevy Astro brakes sticking

Who installed the hydra booster? Did any power steering fluid get into the master cylinder from the old unit? Remove the cap on the master, is the rubber seal swelling? If yes, then the brakes fluid became contaminated and All rubber parts need to be replaced, this would include the master, calipers, wheel cylinders, flex hoses, and combination valve. Remove a small amount of brake fluid, put it in a cup of water, swirl it, it should be milky white, if oil beads appear on top, the fluid is contaminated. If the fluid is OK, When the brakes lock up, jack a locked wheel off the ground, open the bleeder screw, if the wheel turns freely now, replace the flex hoses, if it stays locked, replace the calipers. Also check the pushrod length, this is the rod that comes out of the booster, and pushes on the master, if it's too long, brakes can lock like yours are. Overheating could be because you are working the engine too hard with locked brakes.