Hydroboost engaging without pedal

[Project_Gotham]

Took the car for a shakedown run and it seems to be fine until after 15 minuets of driving. Seems as if the breaks are slowly dragging progressively to the point where it comes to a complete stop, without pressing the pedal, from a 5 mph roll. Then I shut the car down, restart and it goes away until another 5 mins of driving. Any ideas???

Maybe a back pressure issue? DO I need to vent the res cap? I saw one post where they eliminated the "T" from the low pressure side on the HB and steering box and ran dedicated lines for both on the PS reservoir.. I am not using a PS cooler.

I did hear some type of burping noise when I shut it down but I am unsure if that is from the PS fluid or the PCV issues that I am currently trying to work out.