So I haven't had time to work on the truck for awhile, finally got time and got her started. New lift pump, new fuel filter, did the fuel heater/water in filter sensor delete, new lift pump fuel line and filter head to ip line. Had the fuel tank switch on the front tank which is full. Cracked an injector line and cranked for 30 seconds, let her rest for 2 minutes, cranked again, rest. No fuel to the filter, nothing coming from the lift pump. Thought great, didn't fix it. Then had a thought and switched to the rear tank which is 1/4 full. Cranked for maybe 15 seconds and she fired right up. Tightened the injector line and she's purring like a kitten. Switch to front tank and runs fine. Shut her off, let her sit for a few minutes, try and start and she won't start. Switch to rear tank, starts right up. So here's my question: why won't she start on the front tank but will run on the front tank? Bad selector valve? Or bad sending unit? Or neither?