You're right my tires are 30" high so with that calculated at 65 MPH my engine is turning 2567. BTW tires also hold 80psi. That wakes them an explosion waiting to happen.
Actually E rated (10 ply rated) tires are rated at 80lbs for the maximum rated load. The wife's horse trailer pulling 2015, 3/4 ton and my backhoe pulling 1 ton normally run 80 lb. The 51 3600 with e rated tires I usually run about 45 in the front and about 35 in the rear since it doesn't carry the rated load, works fine.