Engine problem on 1996 chevy van with 350 vortec?

1996 chevy express van runs fine one minute than out of no where runs like crap. No check engine light is coming on fuel filter new fuel pump,plugs wire cap rotor, spider injection, map,tps,crank,coolant temp, mass air is all new and it is still doing it also replaced bank 1 sensor 1 and bank 2 sensor 2 even ran it with the cats off and no change. Got any ideas thanks in advance.