I think it's just our ecu's making crappy maps. For some reason they programed our ecu's to put out sub 10.1 a/f ratios. I think they just get worse the longer they have to set themselves. Try reseting your ecu back to the factory maps.
Just undo the neg. terminal on the battery for a few min. Worth a try anyways! The only other thing I can think of is that the gas companies are adding more and more ethenal into the gas without us knowing it.
not a bad suggestion... i will try it right before my next fill up. you could be right about the gas comp.. i dont know how gas prices are around you but here in ct they have dropped a couple cents. i think they are just put bad fuel in the tanks. thats jmho though