Honestly, I would not worry how fast your coach goes up mountain grades. I drive our 1996 gas coach by rpm on cool days and by the transmission temperature gauge on hot days.
Our 7.4L Chevy has max torque at 1400 and stay pretty flat until 3200 rpm. So I drive it no faster than 3200rpm climbing grades. If the transmission temperature climbs over 160 degrees (measured after the cooler, with the cooler fan on) I slow her down.
I believe the 460 Ford has a higher torque number but around 2500 rpm. I would double check I drive accordingly.