I wont stake any money on this diagnosis,,cos it's across the internet after all,,,,,but i would be thinking,,,your cam is fine,,,albeit,,maybee a little lumpy for a street car with stock ignition,,,,what Rpm's are you running when it's at 15 pounds,,,and then what Rpm at "0"???
sounds typical though,,,,Higher lift and longer duration cams will make the engine breath a whole lot better,,,but the piston is like a compressor pump working in reverse,,,it has to suck atmospheric (air) to develope vaccume for the rest of the car,,,,longer durations on the cam will hamper the motors abillity to develope sufficient vaccume,,,,,thats why older cars with vaccume wipers and such,,would have the wipers stop in mid stroke when revving the engine,,,you can purchase a vaccume amplifier motor to attache to your engine,,,this will solve a few problems i'm sure.
But do check your coil as well,,and make sure your getting vaccume advance.