Front Disk Brake Problem

[72super20]

I recently put a new power booster on my 72 Cheyenne Super 20. The brakes were stronger.....but now they tend to build up pressure and not release it. The front wheels will totally lock until I bleed off the pressure.

I did have to back the brake light adjustement off about a 1/4 inch after installing the booster.

Is it possible that the booster and master cylinder for the 72 - 3/4 ton can have different possible combinations?? Is there any type of check valve in the brake system that could cause the pressure to not release??