I dont think that the DP could affect the vacuum........just would possible affect how much boost you have at the high end........I think the brake booster is just that. It(through vacuum) assists your brakes so that they are not manual. If you dont have enough vacuum(through a leak or through something like a large cam) your brake assist will not help you as much or at all....This is just the largest vacuum line and that is where I would start. Do the spraying carb cleaner trick all over any vacuum lines and fittings.........Hope this helps some.....
