Hyboost

I know there have been a lot of fuel milage posts lately, but one more! My wife has a 12 Mazda 3 Sky Active with an automatic.

The first 4 tanks, she avg 31 city and 42 hwy. We both thought that was awesome. Only problem was the transmission was doing some weird shifting. When driving on the hwy, at 65 mph, and if we needed to pass another vehicle, when flooring or almost flooring it, the car will downshift as needed, but when doing so, it slammed so hard that I thought we puked the transaxle all over the road! No kidding, it slammed so hard it actually felt like the wheels chirped! So for the rest of that trip, i didnt dare floor it again. But when close to home, I tried it again, and it slammed just as hard. I took it to the dealer and they reflashed the PCM. This not only solved the problem, but the car seems more responsive during everyday driving. So we were both happy. Until we checked our milage on the next tank of fuel. She dropped down to approx 26 & 30 MPG! We were shocked that a reflash could hurt our milage so much. We are on our 2nd tank since the update, and are on par with the first. It is much colder this week, so that might have something to do with it. But I was wondering if anyone else experienced this after a reflash for the tranny concern? I'm afraid what is going to happen when we switch over to our 4 winter tires next month.[