It’s NOT a bad lift pump which is only used for starting the engine... learned that the expensive $$ way. I had the same problem and by putting a short length of clear plastic tubing ($5 in hose, pipe nipple, & 2 clamps) after changing the lift pump, I could see small bubbles in the fuel with lift pump running and the engine running. A big change in temperature made a fitting (which was tight) at the tank start leaking. Removing the hose and putting back on (not as tight) solved the air getting into the fuel which gave me full power again.
Spend $5 putting a clear hose at a fuel filter to check for air in the fuel system.
