F350 Super Duty vs 3500 Denali vs The Ike Pulling 30k lbs

I've been screwing around with the numbers and I think the Duramax time was not really that far off what should have been expected based on a 39000 lb truck and trailer and 2220 ft of elevation gain climbing the hill. Based on those same numbers the Ram should climb the hill in about 12 minutes. The thing that doesn't add up is that the Ford should not have been able to climb the hill in 6 minutes and 20 seconds running at the rpm it ran at unless it is putting out more power than Ford claims.