I have a 1996 3500 dump truck that all of a sudden lost engine power truck is bone stock with a 5speed 120000 miles on it. Truck is not mine. Fuel filter was change out. The truck lost engine power cant even pull a hill only in 2nd gear. The Watergate rust open took that off wired it close it help a little bit. The truck was to a shop they said it need an injector pump but I am not sold on that. I am thinking theres something wrong with AFC housing or fuel issue. Would the fuel shut off do this?