1982 GMC Brakes locking up??

My 1982 GMC 1500 didn't have power brakes and the brakes would act as though they were engaged on the front. I wanted to change to power brakes anyway so I added a vacuum booster (everything from the brake pedal out) and master cylinder from a wreck. I also replaced both front calipers,brake lines and pads.(all new) Everything worked great for a couple of days, now the BRAKES are back to doing the same as if I've got my foot on the brakes. The little six banger can't handle much more of this, anyone know what might be causing problem??????????