New build- brakes won’t release

[Low Elco]

Hi all-

I finally got my 67 swb back on the road and it’s pretty good except that the brakes will immobile the truck after a few miles and be smoking! I’ve backed off the pushrod so far that the pedal arm doesn’t hit the stop pad. Still does it. Here’s the setup- 71 stop plate and pad, 71 brake pedal return spring, custom link sleeve, captain fab bracket, aftermarket s10 style dual diaphragm booster, cpp vette style squashed master, wilwood adjustable f/r valve, all new nicop lines, 3/4 ton calipers, stock narrow drums in the rear. They work great, except they seem to retain a bit of pressure every time you use them, until they get real hot and you don’t go. It’ll drag it down against the motor. Crack the bleeder and pop the pressure, back in business. Any ideas? Thanks, chip