Just brought out my 01 DeVille from storage. When it is showing the MPG or in metric L/100km it has "INST" after each one. I can't remember seeing this before. Is that normal or not? Also what does it stand for.

Yes, that's normal. It simply shows you that "instant" on how much MPG you will get on the current conditions for that moment in time.

Use the INFO button to toggle to AVG (average) or what ever else you want on the screen.