not to brag but since I intercooled my 4Runner(and did some other notorious little mods here and there), i can get 100mph when empty or about 90 when rigged to the roof with gear like in the last pic on straight road! it seems not too bad for a stock mech diesel which does pretty good uphill! I dont get the average 24mpg tho, when I go 100!
and also only in stock tires and the quality of fuel vary badly over here. my last trip was 220 miles and I only got 15mpg!
Unlike the more modern D4D toyota engines, the mech diesels are very capricious to the quality of diesel and tend to perform badly when fuel is bad, but not sensitive, meaning it wont be damaged by the poor grade fuel.
So my advice is if you know your 4Runner is running smooth and nothing is wrong with it, hp and torque would only be degraded from the quality of fuel...but I think gasoline is pretty good quality in the US compared to here! and a lot lot cheaper! long live second amendment!