Your answers will be very subjective from one person to the next based on everyone's personal feelings, taste's, and opinions. Not everyone's answer will be the same just as not everyone's answer will be right or wrong. To some, an extra $1k-$2K over the life of the truck after trade in is worth the added power and ease of towing, to others it may not be.
There are some objective answers to your question regarding cost, but that will also vary depending on everyone's location. Some like me only have around a $.40 cent difference between diesel and gas while other like yourself may have more than a dollar.
Although, I will say that the higher the fuel cost in general, the more you will benefit from a vehicles that gets better fuel mileage. For instance, a Ram 2500 Cummins gets an average of 15.5 mpg while the gas version is 12 mpg. With that, if diesel is $5.19 then it would cost $.34 cents per mile while the gas version will be $.35 cents per mile with gas being $1.04 cheaper at $4.15. If both gas and diesel were exactly $1 less then the gas truck would cost per mile of $.01 cent less than the diesel. So as fuel prices increase, it benefits the diesel due to it's better fuel economy. When they decrease, then they benefit the gas. Kind of the opposite of what most people think.