Sometimes you have to eliminate everything else it could possibly be. You need some gauges, EGt, boost and fuel pressure at minimum. You also need to verify timing and bump it up some if possible. Slipped timing will cause performance issues as will low fuel pressure, so I would verify fuel pressure is in spec and timing is right. Also, what have you done to modify fuel? These engines are borderline gutless completely bone stock. Once you feel you have eliminated everything it could be other than IP, then take it off and take it to a reputable Bosch pump shop and let them bench test it. Bench testing is not awfully expensive, but once they start going inside, the dollars can start flowing freely, but once again, verify fuel pressure and timing.
'96 Dodge 3500,KDP killed, boost-pyro-trans temp, not stock anymore
'01 Dodge 2500 4X4, EC, LB, 6 speed, FP-pyro-boost,
'97 Chevrolet Suburban, K1500, 4.10 gears