Hoping things change!
There are many factors that need to be considered:
1) The fuel economy gauge displays a running average; it's not instaneous f/e. So, driving downhill, the displayed economy should improve, but it will be weighted by the previous economy and distance.
2) The fuel economy gauge may not be correct, or it may need to be reset. Try a regular ol' hand calculcation: fill tank, drive a bunch of miles, fill tank again, divide miles driven by qty of fuel.
3) You need to reset the odometer to reset the gauge. For the Sacremento-to-Reno run, try resting the odometer in Sacremento, logging the mileage when you arrive in Reno, and then resting the odometer in Reno to get the downhill number when you return to Sacremento.
4) Fuel economy may improve with age.
5) I have to ask: Are you using the correct grade fuel? The turbo motor requires premium fuel (91 AKI min)... using 89 or 87 will result in reduced fuel economy.
6) If the outside temp is 32F or higher, the a/c compressor will run if the defroster is selected.
7) Check tire pressure when the tires are cold; i.e., in the morning after leaving the car out overnight.
Jim / crewzer