Pedal to the floor

I just did some major brake work on my Duster, installed a rear disc conversion kit, all new lines, front calipers and rotors and new master cylinder all from Right Stuff Detailing.
After stopping leaks and bleeding the brakes I can sit and pump the pedal with engine off and have a good firm pedal, but start the engine and it goes straight to the floor. The car still seems to stop ok (never got it above 5mph), but there is no pedal feel at all.
These are power brakes, and I did not replace the booster. It seemed to be working OK after I did my engine swap from a slant to a 408 small block. I know that a larger cam will hurt the performance of the booster, and I did unhook the vacuum line from the booster and drove the car a tiny bit and had good pedal feel there.
Do I need to replace the booster? Or is there something else I can do to give me a firm pedal with the vacuum hooked up? Everything is new and installed/adjusted properly. I'll be giving Right Stuff a call in the morning to see what they cam suggest.
Thanks!