> water and weight, and luggage/gear. We averaged about 17mpg at about 70mph
> for the first 250 miles.

Try following trucks!  ;-)
>
> Also, has anybody had any problems or benefits from running 92 octane fuel
> when on long road trips?

There is always someone who wants to argue with me, but there is NO
benefit in running a higher octane than the book calls for.  You are
just throwing your money away.  Octane SLOWS down the burn rate to
prevent knocking.  If you are not knocking, you don't need it.  And if
you are knocking, you need to check your timing and a couple of other
things.

 Is 70-75mph a healthy driving speed when on flats?

How close to wide open are you?  Quite healthy if you are not at the
limits.  If you reduce speed to 60-65, your mpg will improve
dramatically!  (or follow trucks).

TBill

***Honk if you love peace and quite***