icanfixall
Official GMM hand model
Heres a thought. A while back a member had shuddering issues at idle and low power. He replaced everything. finally found the rubber hose from the frame to the mechanical lift pump had a kink in it. That hose takes a beating flexing all the time. Usually the crack and you end up sucking air. I suggest no matter what you replace that hose now. Its probably original and sucks flat when you run the engine.