H Pipe/X Pipe Question...

[bmxelvs]

Please bear with me as this post will be a bit long... First off let me start by saying I just bought a 2000 Mustang GT with lots of mods already done... Problem is I dont know what all was done. The car has ceramic coated long tube headers on it and it had a X-Pipe with cats on it when I bought it, but it wouldnt pass smog so the dealership pulled out the pipe and now it has a H-Pipe with cats on it. Here is the weird part, when I got the old cats back from the muffler shop, one of the cats was a dummy and had been totally gutted while the other one had not... Same serial number on both cats and it is obvious that one has been opened up and re-welded. Why would you have one side with a cat, and one side without? Does one bank just naturally flowbetter and require some back pressure? All I know now is that the car is way quieter, and has dropped a SIGNIFICANT amount of power, and revs slower. What do I do to get the car back to the way it was? Any input would be greatly appreciated.