Title says it all. New Bosch o2 sensor to replace what was probably the original and my mpg has decreased slightly. 93 4.0 a/t no driving pattern changes. If anything it should have been better because I did a lot more highway driving this tank than usual. Not sure why this would be happening or what to start looking for.

 

I'd try resetting my ecu. Unplug the battery for a few minutes. If your old O2 was bad the ecu could have been compensating.