2001-3/4 ton 6.0 hesitation-Stumped

My hesitation or no power comes when the vehicle gets over 45-50 miles per hour, otherwise it drives just fine--It is throwing the code misfire and egr valve. I figure that I will replace the plugs first and check the wires because the egr valve is expensive. Am I headed in the right direction? Can the egr valve be cleaned and can an egr valve code be caused by a multiple of different things?--- Please help--I will post any solution--Thanks

I am recieving engine codes po300 and po404(misfire and egr valve)but I can push the pedal to the floor and the engine revs but no go, could this be a torque converter problem or a transmission problem, or maybe a dirty trans screen. The engine runs out just fine.--still stumped

clogged air filter was the problem