Cm870 running like it out of fuel???

[W9L]

Had a very similar problem with a cm2350. Found one tank vent questionable. Also had a blubbering idle that would make you wonder if a valve wasn't seating properly or spring broke. 8 yrs old so I changed out all fuel lines, vents, and new return splitter. Truck has never ran smoother or quieter at any speed. Been getting a fuel restriction code and I guess, a derate that would cut it to 40mph. Pull over, shut it off, wait a couple minutes, fire up and go on for a while. Always happened during high fuel demand.