Ok it seems I have had a significant drop in gas mileage since I tuned up the car and put the O2 sensor in. Its not terribly worse, but noticible. The only thing I can think of is before I changed the Bosch O2 it had no power, but had outstanding MPG. The Bosch must have been running it lean which would cause the excellent gas mileage and the loss of power. Not that I got the AC in, it bust have gone back to the right mixture, now I have tons more power, but worse gas mileage. Does this make sense? Is there something else that would have caused this? Please advise

It might need to relearn the new 02. It could be running rich right now because of it.

Not sure what the exact mileage is, I know I put 100 miles on since I filled up friday, and today it took 5 gallon to top it back off, I only drove that 100 miles, Before it would be 200 miles or more before it would need $10 bucks worth of gas. I drove mostly highway this weekend. How long does it take for the computer to re-learn? I put at lease 500 miles on since I put it in a couple weeks ago?

Other than worse gas mileage, its running great, has more power than it ever has.

Yeah, it must have been running pretty lean before cause like I said, it had no power, like less than a 4 banger.