Engine cranks but will not start

Hey everyone, I'm a newbie to DIY vehicle maintenance so please bare with my ignorance. My plow truck was running fine this summer; however, a month ago it would not start. Battery is good, has good spark, and both fuel pump assemblies are running. I started by spraying starter fluid in the intake and the truck starts for a short period. Next I followed the gas lines and found the return kinked and leaking. That has been repaired. I removed the tank selector assembly and cleaned the internals, diaphragm was intact. Then I replaced the fuel filter. Still no start. I found the high pressure in-line fuel pump wire harness had been chewed up. Wires have been fixed and HP pump replaced, just in case. Still no start. I have fuel to the Schrader valve and I am replacing the fuel pressure regulator tomorrow. I'm at a loss, any suggestions would be appreciated.