Here's something most don't consider. If you're buying a new truck every 2 to 5 years, you probably will not see a cost benefit to diesels. Where they really shine is longevity/durability over the life of the truck. With proper maintenance, they will out last a gas truck by years.
I'm from the drive a vehicle until you're pushing it camp. I'm on my 3rd diesel. None were bought new, and only replaced one because the family out grew it. Still have two of them. The one I sold had just over 600,000 miles on it. My 92 F250 has 140,000 and my 07 Dodge has 125,000. Not a thing wrong with either of them. The F250 will be passed down to my son. I expect he'll get another few hundred thousand miles out of it unless he gets tired of driving slow (7.3 IDI will never win a race).
If you're gonna be replacing a truck after just 5 years, then a gas truck may not be a bad idea money wise. New gas trucks are getting really good with torque and horse power, so if you're not pulling a huge 5er, probably don't need diesel.