I see I'm kinda late to chime on this thread, lol. You need to check out the turbo diesel registry, great site, great bunch of people and ton's of information.
My 00 Dodge had the 5.9 inline 6 TD Cummins, great motor currently has 257,000 miles on it and still running 40+psi of boost

:rock: I did a bunch of work to it as things wore out, only real bad thing was the tranny, I'm on my third. I did an ATS Diesel stage 5 this time and its been great. I was towing my 26' trailer then replaced that with my current 32' that now holds my Harley, SRT-10, displays and whatnot, prob 15k lbs. Great truck, ton's of power and oh so much fun to drive with out the trailer. Loved blowing smoke in everyones windows
If you go the mod route, do the injectors(I did KAX motorsports 90LBS but I've seen many guys going the Cummins marine route, a little cheaper and more power) will wake it right up, the Edge juice with attitude, adjustable and allows you to monitor everything, MBRP makes a great exhaust for it and ATS makes some high quality parts.
The Mega Cab is quite roomy,I think you'll be happy with it. I opted for something bigger and did the Kodiak, really nice truck but no where near the power out put of my 3500 Ram.
FYI I've just got home from a cross country trip, just about every truck stop had LSD so that's not a problem, legaly they must have it now, just need to put some additives in it to keep her lubricated, Bio-diesel is awesome, wish I could find here in MD