Aftermarket Power Brake Problem

[NW Task Force]

I am running an aftermarket under-cab 7" power brake unit that uses the OEM style brake pedal lever that hinges forward and down (just like the stock brake and clutch pedal). I am running disc brakes at all 4 corners. Basically, my pedal does not return back up on its own after pressing the brake. It seems to stick in the partly applied position, therefore dragging the brakes. I can easily take the tip of my shoe and pull it back up and feel the brakes release all the way. Sometimes the pedal will return correctly on its own when I tap the pedal hard to the floor.........????? This brake booster unit is only 1yr old and I have tested it for vacuum (18 hg) and the pedal is hard when the engine is not running, when started it immediately moves down (seems correct). I did a little reading and it seems some hot rodders online do add on "brake pedal return springs" from time to time. This seems like a simple solution, but is it covering up a bigger problem? Anyone else experience this?