Truck runs (poorly) then stops. We've replaced in tank pump, in line pump, filter, relay and fuel pressure regulator (twice). The first time the fuel pressure regulator was drawing fuel up into the vacuum, this time it's seeping in the middle. My question is--could a clogged return line cause this? And, what controls the pumps--the ecu? Are they supposed to run constantly? Can the ecu tell them to run too much and build so much pressure they blow the fuel pressure regulator?