I've never seen my trip computer read 29.1 .
I have seen my 2013 2.5X with 4 speed A/T hit 31 MPG briefly on the mileage computer on a few occasions of highway driving. That was driving 65 on cruise, tire pressure 32psi all around, windows up, no A/C on, no cross-bars on the roof rack. It was never quite that high by the end of the trip.
But I have also learned that my trip computer is consistently about .8 mpg higher in it's mpg reading compared to the gas pump refill calculations after each trip. I use the same pump at the same station 95% of the time. If my trip meter says 30 mpg after 300 miles, my refill calculations will come out to about 29.2. This .8 difference is pretty consistent after 2-3 dozen refills, whether it is mostly highway on that tank or combined.
The refill math may not be an accurate method for an individual tank of gas, but after several refills at the same pump it should be fairly accurate, since any variations in pump shut-off will impact the next tank in a way that self-corrects for average accuracy over a period of several refills. At least in my brain, that makes sense. This assumes an accurately calibrated gas pump of course, which is not guaranteed, I suppose. I should probably check the date on the pump calibration sticker next time I use the pump. Sucker could be cheating me a bit.
Either way, I am happy with my (optimum) 29+ on highway trips and 25.5 combined over 11k miles. I didn't see highway numbers that good until about 3,000-3,500 on the odometer. The official break in may be 1000 miles, but there was definitely an extended performance/mileage break-in on mine that lasted at least 3,000+, where mpg and throttle smoothness/responsiveness kept gradually improving.
Putting my 17 foot long sea kayak on the roof knocks roughly 3mpg off the highway efficiency in summer, and I'm sure the bars and kayak saddles alone have a slight negative impact if I leave them up there. The wind noise from them tells the tale. I saw a drop of about 2mpg on a highway trip when temps were in the 30's vs. the same trip when it was 60-70, all other factors being the same, so weather does matter.