Intermittent loss of power

My truck intermittently throws a check engine light, driving or not. Shortly after the check engine light comes on the truck shutters and loses power, will sometimes stall, on accelerator or not. Sometimes the truck regains power only to lose it again. I've replaced the fuel filter, map sensor, distrubutor, cap, rotor, some wires, coil pack, oxygen sensor, egr valve and egr solinoid, hooked a fuel pressure gauge up to the fuel rail and the pressure never dropped below 30 psi even while it was shuttering, even when I gave it gas while shuttering. I even cut a huge hole in the side of the pre-cat thinking that It's honeycomb broke off and clogged the cat. It did but I ran the truck with the exhaust dumping out of the pre-cat, still same symptoms. The temperature gauge never reads that the truck is over heating. I'm lost. Help please someone. Thanks