here is what was told to me by an exhaust shop. if ya cant get rid of the cats dont mess with the ones on the truck they like a look good design wont get any gains noticable for the money. go to magnaflow hp muffler. 2"-in and 2.5" out, no resonator -straight pipe out to a resonator 3.5"S.S. tip. please let me know what you think. thank you.

cheapest and bet way to get HP/torque gains. Just make sure you can get mandrel bent tubes.

Another quick, cheap solution is replace the muffler like you said, and cut off the resonator in back and replace with a straight tube. You don't have to worry about the bend over the rear diff then.