Hello acy76. I recommend that you purchase a new diesel filter , a clear inline fuel filter, a box of fuel hose screw clamps, some diesel cetane improver and injector cleaner and a piece of fuel line hose about 3 feet long.............get a plastic container that will hold about a gallon of fuel......secure the container under the hood and run the hose from the container to the IP with the inline filter (bypassing the main filter) and run the return hose into the container.........plug up the block heater for about 8 hours then crank the engine and let it run with fresh fuel and cleaner mix............

The basic idea with this is to work from known good values (the engine runs ok) backwards to the fuel tank(including the gas tank cap)

If the engine runs ok, then put the new main diesel filter in line with the plastic tank.........

If it still runs ok, drop and clean the fuel tank and fuel line from the tank to the engine..........

I would also install a electric pump (3-5 PSI) at the tank at this time as well......especially if you have plans to use bio diesel or VO.........

If the engine does not run ok from the plastic container.......just stop and leave it in place and report back.............

regards,
crossbones