My car stumbles and I have to work the throttle to keep it running. Won't stay idling. It's a 70 Challenger with a 5.7 with a cam headers etc, and is running on the factory computer with tune for the cam. It's been running fin for 5 years. Recently changed the tank with a in tank pump. Still ran fine for several months, but not anymore. I checked the fuel pressure, it's at 50 psi. I'm thinking it's the LS filter, or cheap pump that came with the tank. Is 50 psi so low that it might cause this issue?