Handling could be better or worse. Based on the original suspension design, raising or lowering changes geometry and center of gravity. How it reacts is all about what you do and how its originally designed. I've driven vehicles that handle horribly but the owner thinks its fine.
I bought an 04 TJ some years ago. 4" springs and shocks. It was almost undriveable at 60 mph. The lift was professionally done, but not done correctly. I rebuilt everything and when it was done it actually handled better then stock. with about 6" of lift and 35 inch tires.
Fuel wise, its all about additives. A good example is alcohol. The more they put in, the lower the milage. Summer vs winter blends also. What's sad is most of the additives put in are due to politics and data based on a 70's vehicle. If you live in a state that runs just gas without alcohol, you not only get better milage but you put out less emissions then the "clean" alcohol based fuel.
