Over the years I've owned the Ford 7.3 and 6.0 diesel, several Duramax's and a Dodge Cummins 12valve, after running diesels for 13-14 years, I'm done with them, unless you drive them until they absolutely fall apart you will never recover the extra expense of upkeep, higher fuel prices, just the additional cost of parts is nuts, price a starter, or a set of injectors. I've went back to gas and will stay there forever, and yes, I tow a bunch of heavy loads.
I would send your trucks computer to one of the tuners that others have mentioned. Tell them exactly what you want out of the truck, the guys doing the custom tunes can boost your trucks performance a heck of a lot better than a off the shelf tuner. I bought my 3500 HD 4x4 with a blow 6.0, a lady had run it into a fence and cut the lower radiator hose and ran it until it fried.lol I bought the truck out of a salvage pool with minimal damage, front bumper and grill were damaged along with blow motor, for 2300.00, I found a 5.3 on CL for 400.00 that only had 7000 miles on it, we put it in, had a about 50 miles from us tune the computer for towing, and the little 5.3 has done a fantastic job, our 4240 JD with fluid in the duals and wheel weights is close to 18k lbs along with the 24' dovetail gooseneck trailer and it handles it fine. Our truck has 4:56 gears in it though. Although we haven't been dyno'd the guy thinks we are cranking out around 360-70 hp out of the little 5.3. The 6.0's I've been around have been good engines, I've had one apart in the shop and they are extremely well built compared to the old small block's.
If I had to go back to a diesel truck it hands down would be a duramax with the Allison tranny, it was the most trouble free of all the diesel trucks I ran. The cummins is a great engine, but it is surrounded by a Dodge, if the cummins were in a Ford truck it would be the ticket. I absolutely love the Allison tranny, it would take anything we threw at it. Dodge may have there tranny issues taken care of , but there front ends are ****, won't take the weight of the diesel in my opinion. Maybe if you just baby them on pavement, but driving them over rough farm ground just results in having them rebuilt every 20-25k miles at 750-1000.00, as a result I hate Dodges.
Get you a custom tune and try it for a while, cheaper than a new truck.