Our old '85 Class C (26') got 6.5 mpg at sea level and about 4.5 at altitude. It was a 460 with a cerburetor and enough anti smog gear for a small city. The '02 Class A we just sold (a 32-footer) got a consistent 7.5 to 8 mpg regardless of altitude.
Most vehicles went to electronic fuel injection in the early 1990s, some of the more tech-savvy manufacturers did it in the mid 80's. Our '85 Camry had it. Many of the early versions had a single injector in the throttle body (where the carb used to be) By 1998, they were pretty much all individual port injection.