Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Ok let me opt out to see if someone with more experience with diesel engines can help you
Unhook the tank side of the fuel line at the filter underneath and blow air with a compressor back into the tank with the cap off for about 30-60 seconds .
Could be multiple things. Moisture in fuel. Wiring issue to pump, making pump not pump constantly. Also check your fuel cap. when it starts being sluggish, remove fuel cap to make sure venting is not the issue
May need to bleed the fuel injector lines, could be getting air in lines. Just trying to throw some ideas out there for you. I would start with the fuel cap removal as it is the easiest and its free.