As I have posted elsewhere, I have found that on an incline I see better instantaneous mpg when climbing in 5th gear than if I change down to 4th. I have a ScanGauge E fitted to my OBD2 port, and it is the best thing ever for improving fuel efficiency, when a car does not have onboard instantaneous mpg display.
It shows when car is in
Deceleration
Fuel
Cut
Off mode, which is a must for getting good fuel consumption, as well as letting you know when you are using a lot of fuel and when you are saving fuel.
The display is user configurable, with a bar graph showing how well you are doing against your current average. As you can see I have mine set for instantaneous mpg and journey average, but you can display coolant temperature, intake air temperature, Manifold Air Pressure (as a vacuum gauge tells you), in fact, any two from eighteen parameters you can display. It records and displays a range of data from the current trip, today, previous day, this tank and even an estimate of miles until tank is empty. It also displays and resets OBD codes, when required. At just under £100 I found it money well spent.