I would check everything before the lift pump.
After the lift pump the fuel pressure should be at least 6# and will show a leak.
We had a diesel genset installed last year. There's a dedicated pickup from the fuel tank, that goes a few feet to the primary fuel filter, and then another 6-8 feet to the genset. Genset is only a foot above the fuel tank. When the genset is unused for awhile, I have to bleed the fuel line of air bubbles. The dealer can't seem to diagnose the problem. Any suggestions?