This one has got me puzzled,6.0 litre efi ,had to be towed home,would start but not enough power to move,checked fuel press.20-23 psi with or without regulator vaccum line on,dual tanks,pumps were replaced at dealer 2 years ago,replaced filter,no improvement.

 

PUMP IS BAD...only 1 pump makes psi to send to the engine...the aux pump just movesfuelfrom tank to tank

 

Thanks,problem solved,pump was bad sock was also full of mud and rust,found cut filler neck vent hose behind rear tires,also rusted fuel lines from front tank to fuel filter.WOW not a cheap fix.