I am trying to decide between a F250 (1999 with 105K) with an automatic transmission and a F350 (2002 65K) with the 6 speed manual transmission. Both trucks are equipped with the 7.3 liter Powerstroke Diesel engine and are in great shape. Under the same driving conditions, will I get better fuel mileage with the 6 speed manual, and if so how much and will one transmission hold up any better than the other?