Heading east on I-70, making the long climb to the Eisenhower tunnel (11,150 ft elevation), towing a Camry on an Acme dolly.
The final couple miles was in line with several semi's, I force it into 1st gear, and then just hold between 3500 and 4000 rpm. No problems with heat, and still have plenty of throttle left in case I need it.
(2001 Ford F53 with V10 engine)