it's a slow night, plenty of time to waste crunching worthless numbers, soooo,
mathematically a 26.8" tire would be 2105 engine rpms @ 60 mph with 3.73 gears and .75 overdrive transmission.
in reality tires and tachometers vary a bit, sometimes a lot.
if you too have time to waste it's easy to determine the data. 60 mph is an ideal speed for calculating since 60 mph equals 1 mile per minute.
these numbers are based on a approx 29" tire, yours may be smaller/larger.
mark a rear tire and roll it exactly 1 revolution, it will be in the vicinity of 90 inches. (you can count driveshaft revolutions to verify gear ratio)
divide by 12 to find feet per tire revolution, around 7-1/2 feet.
divide that into 5280 (feet per mile) and you get about 700 tire revolutions per mile at 60 mph so tires are going 700 rpm.
multiply that by rear gear ratio, 3.73 which is driveshaft rpm of around 2600.
multiply that by the overdrive ratio of .75 to get 1950 engine rpms.
that's about 8% less than your observed readings.
and it's still a slow night.