it acts EXACTLY like it did b 4 after replacing all these parts? & you hooked a gas can 2 the mech pump inlet & no ch? Std p rod length is 3.250" so I dont think .030" shorter is killing you. I'm gonna go out on a limb & say that the new pump is malfunctioning which is confusing the issue because everything was replaced right? & you wouldn't think the new pump would b the prob that it has 2 be something else but there ain't nothing else unless we're missing something. The can/hose on the inlet elims everything rearward. The cam lobe/purod are solid & will b constant as in if the stroke was too short it would still stay at a constant (but too low) psi & not drop. That only leaves the pump & I had one act like that. If it's a rebuildable one open it up & see if anything looks out of whack & I'm assuming not an oddball issue like E10 vapor locking but it happens pretty quick?. Holler when you find something but I bet on the pump