I am going to guess that there is nothing wrong with the pump or pressure tank. You may have a blockage in the fixture that is getting low flow (may not be low pressure, may be low flow). Faucet aerators often get clogged with debris, and the faucet appears to have low pressure, when the real problem is simply debris in the aerator. Similar problems can occur in showerheads. A simple check is to remove the aerator, if the problem goes away, you have found the issue, simply clean or replace the aerator.