Once you rule out some kind of ignition problems,; spark plugs and wires, ignition timing, distrib. cap & rotor, the cause may be low fuel pressure from a failing pump or clogged filter. Listen to the pump in the gas tank. If its been getting louder lately, have the pressure tested.
i would also check the oil for radiator fluid or at least keep an eye on it cause a loss of power could also be a blown head gasket
Also check fuel psi regulator remove vacuum line check for fuel leak should be no fuel replace if leaking. FPR controls psi going to injectors low psi low power also make sure you have no vacuum leaks FPR uses vacume to adjust fuel psi.