Don't get excited yet. The job of the check valve is to keep a vacuum reserve in the booster . So long as the engine vacuum is up, the valve goes along for a free ride. If you have a hard pedal with the vacuum up, the valve is not the cause.
So a little diagnostic is in order here.
When do you have a hard pedal?
Do you or did you,ever get boost assist?
What vacuum numbers are you getting from your engine, both at idle and at maximum.