Get the diesel! My work trucks are similar to what you are looking at. Both '04 F250 Lariat, one with the V10 and the other is a 6.0 diesel. For the last few months the fuel cost of V10 has been $150-$200 per month more than the diesel. The V10 gets about 12 mpg in the city... 8 mpg with a trailer + equipment. The 6.0 stays at 13 mpg with or without a trailer. Also, just in case you ever want to sell it... The V10 depreciates rapidly.
Opportunities are usually disguised as hard work, so most people don't recognize them.