I drive 1996 LX450 with 4.88 and 35". 7000Lbs. I get about 11 or 12MPG on the road.
I started from full tank (22GAL) at the closest filling station
I was carrying two 5GAL (so 10Gal), used both jerrycans to fillup the second night.
I drove into Moab on Thu with the fuel light on.
I don't remember exactly how much I put in once I got into Moab, but IIRC it was 20Gal.