1994 Chevy Cavalier fuel pump

It really doesnt sound like a fuel pump. Usually when they are bad, they are bad all the time. If it is consistantly starving for fuel after 20 minutes, it sounds more like you may have a bad fuel cap. If your tank is not venting, maybe it is building up back pressure and not allowing the fuel to flow properly.
It is atleast worth a try, and a whole lot less money and trouble than changing a fuel pump and finding out it is not the problem.
It looks like your fuel pump is in your fuel tank, and requires tank access to replace. Your fuel filter is located under the rear of the car, reward of the fuel tank.
Are you sure it is starving for fuel, and not overheating?