Lower MPG after I changed my O2 sensor (Oxygen Sensor)

Hey guys,

A week ago I was working on changing my transmission mount on my car. While I had the battery taken out i decided to change the O2 Sensor to do some preventative maintenance. I've noticed however im getting reduced Miles per gallon. I havent finished my full tank yet but my needle is lower than it normally would be with the miles i have. Has anyone ever experienced this? I'm going to keep monitoring it but it seems odd. My car does feel like it drives and idles smoother now but what i perceive as decreased MPG's is weird. I replaced it with an NTK sensor.

Old is on the left and the new NTK is on the right.

could be the ecm relearning the fuel trim and mapping of the vehicle give it another full tank and re evaluate 02 sensors can cause that in the first tank or 2 on some cars