It's sucking ar somewhere and I've replaced 80% of the steel lines and all the rubber hoses from the tank to the injector pump. It will start fairly easy, with a decent amount of gray smoke, but after 10-15 minutes it will start to stumble and lose power. I doesn't die and it seems that if I just drive it in town (30 mph) the symptoms aren't as bad. The only steel lines I haven't replaced are the ones between the lift pump and the filter ( runs in the valley) and between the filter and the injector pump. The air was bleeding through the top of the filter before I put a spin-on one in. What are the common leaking spots?