Kinda sounding like it's sucking in a little air. Put 5 pounds of air in the tanks, and look for leaks. That, or something fuel supply related.
commuter: 08 VW R32, or 67 F100,300,offy intake,edel carb,274* cam,header
Work truck:'94 IH 4900, DTA466 lightly bombed(#0 fuel plate, timing at 22*, 3 clicks tighter gov springs), Allison MT653, Voith retarder, and straight piped