I'd check the speedo and make sure it's correct, along with the tach..... I think 4.10's
I know somewhat apples to oranges, but my 6.0 with 3.73's runs 70 at ~2000 rpm. This is all stock, and speedo confirmed with GPS.
Also, 3.73 would have been a change-out, Ford didn't offer 3.73 factory on the IDI trucks.....