Did the problem just start or has it always been there ?
It may very well be a problem with the piping in the house and have nothing at all to do with the pump.
Quick, unofficial test. There should be a drain valve on the well pressure tank, near the bottom. Put a garden hose on it and turn it on full bore. See what the pressure and flow look like there. If it's good then you have something else going on down the line so to speak. Sorry you got talked into a pump that you didn't need, maybe you can get the well guy to take it back or rebate you some money.