Here's the layout, a little more finished. I tried 4 digits for tank miles and 2 for gallons, but it just looks better lined up I think. And it will be a little simpler to have a function that formats numbers as all NNN.NN.
INstant and CUrrent Miles/Gallon on top
MIles and GAllons for the TanK on the bottom
Enough messing around with the display