No, I'm not inclined to believe that your brake booster is actually pumping the brakes... If it were screwing up to that degree (which would be quite interesting in itself) it wouldn't be pulsing... it'd be constant drag. If it's brake related it's most likely a seized caliper glide and probably in concert with an unevenly bedded friction medium on that rotor. Did the calipers all slide off and on easily? You shouldn't have to wiggle them or pry them off, they should slide easily. Did you lubricate them with an appropriate caliper lube when you reinstalled them? Did you remember to clean out all of the old lubricant?
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