Fuel pump?

so i topped my tank off with premium fuel from Shell... u know the V-Power. well today when i was driving i stopped at a local pub came back to my car 25 minutes later and the engine wont turn over. last night and through this morning the engine was idiling rough, and had a much more aggressive tone to it. even though it did sound better i knew something was wrong. any way i am assuming that it's either a clogged fuel filter, or a clogged fuel pump. more likely the fuel pump. the car is a 1988 Cutlass Cierra 3.8L, its only got 69,9xx miles on it. my question is, is the fuel pump in tank or out of tank, and if it is out of tank is it reachable by just merely going under the car. i know that if u tap it sometimes the pump will break free. i am getting it towed tuesday, today is sunday, but i would like to cancel that if i can drive it up to my mechanic. your responses are much appreciated.

Replace the fuel filter first as it is easiest and cheapest thing to get to. If you have to replace the pump the tank will have to be dropped out of the car as it is an inside the tank pump. I would have to agree that it is probably the fuel pump.