KentuckyCUCV,
You may have a small crack in your fuel system somewhere before the fuel pump. With the thin, easy to pump diesel, it may be imperceptible, but when you get the thicker, harder to pump veggie in there, it may be drawing air into the system that builds up in the top of the fuel filter. I would suggest that you install a piece of clear hose on the return line on the top of the IP and observe it while the engine is running (after a thourough air-bleed session). Any air bubbes passing through the hose mean that you need to get under the truck and follow the supply lines from the fuel pump (on the front, passenger side of the engine) back to the tank. Check the condition of all of the rubber lines, and replace any that look cracked, bulged or collapsed. That should solve your problem.
Next step is to get a heated veggie tank installed.
