Your fuel savings with the ecodiesel will not be enough to recoup the sales tax on the new truck for at least 50,000 miles and that is ignoring the higher maintenance costs with a diesel engine.
I was towing a 13,000 lb. boat and trailer and needed a diesel with my 2500HD but on my last 3 trips the engine went into limp mode and my maximum speed was held to 55 MPH which made for tense driving and freeway merging with the tractor rigs. After the last trip was ended prematurely I stopped using the diesel truck for trips and decided to buy a gas powered pickup to replace it.
What the diesel provided in addition to more torque for towing and the capabilities of the exhaust brake, was 25% greater range on a tank of fuel. Fewer gas stops when towing a trailer and less chance of running out of gas were key concerns. That would also be the case with the Ram ecodiesel with the ability to get a 39 gallon aftermarket fuel tank from Titan Tanks. With the Ram 1500 gas powered trucks the best I can do is a 33 gallon tank and that adds at least $2,445 to the price for the truck and their are no aftermarket options available.