Ya, was thinking the best place for a gage is right of the bleed port between filter and injection pump. Maybe as simple as replacing that bleed port banjo with a gage port banjo (like Genos sells for 2nd gens). Will have to look into this. Correct, with age of these trucks bad seals on the suction line can introduce air, and can lose prime. Sometimes may not leak fuel, but can still suck air.