O2 sensor problems

I have a 01' explorer sport with a 4.0L SOHC. I had replaced the 2 o2 sensors before the cats and the one after, with o.e. bosch sensors. Now the cars gas mileage has gone down. from about 270 miles to the tank and now it gets 200 to 210. any help would be greatly appreciated.

Did you replace the sensors as routine maintenance, or because you had a code? If because of a code, what code were you getting?

Have you scanned for pending codes or checked the operational voltages of the sensors to make sure they are responding and the heaters for them are working?

-Rod

didn't get a code. just did them for routine maintance. i am not getting any trouble codes