Everyone is posting "my truck gets 'X' mpg under this condition or that". Perhaps a better way to consider this is to accept diesel fuel prices are not likely to decrease from their current levels but will certainly continue to rise. Until you have some idea of how many miles you plan to log each year (towing and not towing) will you really have the ability develop a fuel budget..........and even then, if the price volatility of fuel returns like in 2008, you could find a hole blown in your budget projections quite easily.