[sick472]

I've done a bit of testing. I do get upwards of 20" hg while cruising, mostly down hill with light or no accelerator pedal. I did pull the check valve out of the booster last night with the engine idling and could feel/hear no suction through it, but my time ran out and I had to quit for the evening. I'll pull the check valve completely off the hose and see what it does this evening.

I am betting on a bad out-of-the box check valve (like RnR says) as the pedal feels the same no matter what...running, not running, fast, slow, etc. It reminds me of non-power brakes. They stop the truck with no problem, but only with ample leg muscle.