2000 GMC Jimmy no power shakes and stalls

We just replaced the fuel pump because the truck was stalling and shuttering losing power. The problem didn't go away, we hooked it up to the computer and have gotten different codes at different times. We got multiple o2 sensor codes so my mechanich said the new fuel pump was bad, replaced that and codes went away but the trucks still no better, now the mass air flow sensor code comes up. The truck sounds like a popcorn maker and won't go over 30 mph. Initially it runs fine until the engine gets warmed up above 200 then it starts to shutter and stutter losing power. Now what? A friend told me to by pass the egr valve what else can I try?