It's a roots style. Its a very street able safe supercharger. Only looking at about 50hp gains. And yes normal wear can lower rpm needed to achieve pressure.What is your actual MAP throughout the usable powerband? If it feels like it pulls hardest at 5.5K than what you are probably feeling is the meat of the torque curve. However, if you are experiencing low manifold pressure until 5.5K then you either have a centrifugal supercharger that has not been spun into the efficiency range of the charger (a characteristic of centrifugal chargers) or if you have a positive displacement supercharger you have a leak either with the internal lobes of the charger or throughout the intake plumbing. It is also possible that your bypass valve is failing.... These are general places to start since I do not know of the jackson racing supercharger.
The way a roots style or screw style works it literally is two screws forcing air into a smaller area building up pressure. As it continues to do this the screws will wear against each other causing it to not make a tighter seal. Therefore leaking a bit of air as it compresses. It would have to be rebuilt to fix this. Costing 300-800$.What do you mean by normal wear?