MPG being bad and a code for being too rich on Bank 2? Noticing any bogging at low RPMs? Do you feel like you have to clear it before it gets up and goes? It can't be terribly rich if it feels fine. Possibilities: 02 sensor gone bad, you had a misfire or your fuel pressure regulator is on the fritz. I guess I'd rule out #2 since this seems to be a long-term issue. I suppose it could be the MAF, but that would probably throw PO174 as well... If you have cheapo aftermarket plugs, that could also be causing an issue.
In conclusion, you should check: 02 sensors and MAF. These are the easiest to deal with. If nothing, check the fuel pressure regulator, plugs and COPs. If still throwing codes, I dunno? Leaking injector on bank 2?