codes PO430 and PO732

I was wondering how much a bad catalic converter with this code will hurt gas economy and does this have a effect on the transmition. I just dont want to replace it if it is not the problem it is not a cheep fix. I think the PO732 was the shift code I fixed that not cheep either. I guess how much of a problem do I have. The light is not on again. It goes on and off. Any information would be help ful. I bought a hanes manaul and it does not tell me which cat is bank 2. DREW

posted in wrong spot sorry

Bank 2 is cyls 4,5 & 6....closest to radiator.

thanks