I will try some biocide, although if it is clogged I wonder how much good it will do without a physical cleanout.

Could my fuel line routing be causing starvation? The injection pump is located on the driver's side of the engine. I used the existing fuel supply and return lines which run on the passenger side of the truck, connecting them to the pump with rubber fuel hoses that travel up and over the engine on the firewall (similar to the routing of the A/C lines in this area). Is it possible that this up-and-over arrangement is not allowing the pump to draw fuel from the tank?