Poor mileage after O2 sensor replacement

[mtthmpsn]

I haven't been on here in a while as I've had good luck lately with my '06 3.0i (218k miles). That said, service engine light came on and called for bank 2 pre-cat 02 sensor replacement. Extremely easy replacement (replaced both pre-cat sensors), I reset sensor adaptation with INPA, and SES has stayed off.

Problem is, it seems like I'm getting about 2mpg less than previously on the last 2 tanks of gas (same driving habits/locations). Is this due to the adaptation reset and should I expect it to improve? Or due to the sensor replacement itself - I would think 02 sensor replacement should IMPROVE mileage?

Any insight would be appreciated.