I suspect many of us owning diesel trucks are driving far more capable trucks then we need in terms of tongue and towing weight capacity.
I learned a long time again, buy more truck than you will ever think you might need. There were far too many times when my F-150s (1980 versions) were incapable of safely towing off-shore fishing boats. Further, I found my last 7.3L F-250 incapable of towing my fully loaded Hawk camper without suspension mods due to its 8600# GVWR. Not to mention its relatively low GVWC number which made it impossible to safely tow a off-shore fishing boat with the camper in the bed.
Thankfully, current generation Ford trucks (2016+ F150 and 2017+F250/350) have addressed many of the GVWR and GVWC ratings of the previously generation F models.
With Ford now offering far more capable suspensions then any previous generational trucks in the same class, with gas and diesel options, customers now have a much better choice today than a mere 2 years ago to align a truck with their needs.
Upfront costs for a diesel SD is between $8-10K more than a gas truck. I'm on my third diesel Super Duty. The first one I owned for 17 years. The second, I owned for 13 years and the current owner now drives it daily. I'm now driving a 2016 diesel F-350.
Resell value for a well maintained Super Duty (diesel) is exceptional so you recover a large percentage of your upfront costs when you sell the truck. I paid $32,000 for my new 2003 and sold it in 2016 for $23,500. I invested about $7000 in after-market parts over the years for recreational activities. Such expenses are often difficult to recover when you sell. The $23.5k for my 2003 truck was simply due to the high demand of the 7.3 trucks with low mileage, not used for commercial activities. So I had a fantastic ROI on this purchase and the additional money spent on the diesel engine was a solid investment. I'm hoping the same holds true for the 2016 when I sell it in 2031when I'm 78! The 2031 Super Duty will probably be my last diesel Super Duty!
In-so-far as MPG is concerned. I've never kept a fuel log other than to note MPG of the last tank. I do that simply to track which stations offer fuels with better fuel economy. Bio diesel is more expensive per gallon, has less BTU (127,250 for B20 v 129,500 for #2) resulting in greatly reduced fuel economy in my 2016 Super Duty. So I try to avoid B10 and B20 fuels when I can. I also try to avoid stations that have a low diesel fuel demand. Like Jet A fuel (which is diesel fuel, just gone through more filtration) diesel fuel goes bad within 30 days without additives. And many stations (Loves, Pilot, T/A and your local high demand diesel stations) do not purchase diesel additives because they have a high turn over rate in their in-ground tanks. You will know when you have purchased a tank of degraded/aged diesel fuel, your MPG will go way down due to a high percentage loss of BTU.
While I've been retired from the airlines for many years now, I still fly a Diamond DA-42 a bit. It has 2 diesel motors on it. Flying into smaller airports without regularly scheduled airline service requires me to pay particular attention to the Jet A going into the airplane. Simply put, I have to be mindful I'm not getting old, and possibly contaminated Jet A. I tend to carry over aircraft techniques to my truck. Far too anal perhaps, but, flying habits are hard to break, even driving thousands of miles across instead of over Earth. I firmly believe the same holds true for our diesel trucks and getting the best MPG. Avoid stations with a low demand for diesel. Try to avoid bio diesel, especially B20.
I am not familiar with Dodge or Chevy trucks...at all.