I have a 2000 dually that keeps giving code p1689. Sometimes is starts right back up sometime you have to wait a few minutes. When it first started it would be just a quick stumble with no code. I've visually check all the wiring between the vp44 and the ECM, replaced the lift pump, replaced the ECM, and replace the vp44. The problem hasn't changed any. I'm at total loss please help.