Chris replied:

Peter, I assume your 4runner to be a manuel with those consumption figures.
I had a 1993 RV6 (3ltr V6, auto) and my feul consumption was terrible. I suspect that the slightly oversized tires reduced the torque and the engine had to work harder as the gearing was effected.
AFTER adjustments for speedo error of 4.5% due to the larger rubber, my consumption was 21 lt/100 km for medium (no sand) offroad conditions. worse for sand and heavy off road, with the consumption best at 100 km/h on the highway at 16.5l/100km (6 km/lt)
I tried everything: had it dynatuned, replaced the computerised air flow/feul injection meter, airfilters, fuel additives, you name it, but without any luck.
Other than the fuel consuption which was a problem with the range, I found it to be a very capable vehilcle indeed. I did not have LSD, lockers or any other traction control, but did have a OL coil, shock and torsion bar job done, which improved the ride both onroad and off.
Hope this helps