Loss of power

[robbd]

Just recently my engine light came on and it was showing the code P0430, so I went into the exhaust shop asked him to check out for an exhaust leak, which he found nothing, I then changed out my Plugs and wires, and Replaced both the downsteam oxygen sensors, and still I have the loss in power, air filters brand new and I cleaned the MAF just to cover most of my bases. The engine sounds alot louder when I give it hard throttle, but its not putting the power to the tires like it usually would. Im now wondering what it could be? Plugged up Cat? thats the only thing i can think of cause well im not a truck genius. Anyone have any Ideas or have heard of this before ?

[AGT]

Yeah because that code means Catalyst Below Efficient, but you show cats removed in signature

[robbd]

we are removing the manifolds tomorrow, i jumped the gun, ill admit it, the new long tubes are here tomorrow