About the cost difference diesel/gas well I would go with the diesel. The engines is stronger and the pulling power is awsome. You will also have a truck that is worth much more as a trade.
Go look at any of the web sites or ebay and you will see same year model trucks and the gas have really taken a hit. For good reason as well at 120,000 the diesel is at about 1/3 engine life while the gasser is about shot.
The operational cost are big time and really big time towing. The best overall value in a truck is a used diesel in my opinion. I have one setting out on my lot has 350,000 on it and I would drive it to either coast with an oil, fuel, and air filter change tonight.
Go for the diesel either truck will give you great service the Dodge or Ford. One other small issue is transmission now most people don't want to hear this but I have never known anyone to have a problem towing on a standard trans. but have heard story after story of problems with automatics. The exception here may be the Cummings/Allison match that Dodge has.
Just food for thought.