help with my 2008 isx no start..fuel issue??

[shaneco1]

my isx 15 cm 871 i belive i started it the other day and it just slowly ran out of fuel now wont restart so i changed fuel filters filled new filters,,then changed out fuel stop selanoid,,, found lots of varnish still no start,,,took puck out of stop selanoid no start,,,,put new lift pump on it and replaced 10 amp fuse on the motor no start,,changed out pressure valve by the return line..no start..bought a complet icm i think you call it complete from truck yard with gear fuel pump used ,,installed ..still no start,,put a pressure guage on the fitting up by the gear pump only get 15 psi when pump runs ..then it drops to zero when pump stops,,,shouldnt it hold pressure??? i started it sort of on starting flued.. whith the guage installed on lower test port by the selanoids,,pressure got to 270-285psi when on either then it dyed of course uggg,,i am putting fresh fuel from a 5 gallon can to it for now since i think tank bad,,..maybe fuel passages plugged or??? it was running soo what the haa??need some help to figg it out...