high speeds it gets slugesh and dies

by joe jet
(chico cal)

ive got a 79 tahiti with 454 big block . now my problem ia when i get up to speed my boatmotor starts to die like bogs down its like my carborator is cloged .i went through thr carborator new tank new fuel pump new altenator new distributor. the boat cuts out at high speeds it sounds like a disel .then it barley idels like i said it sounds like somthing is cloged in the intake.help...