Are diesels worth it, for costs per mile?

My food for thought: We are an extended summer trip of about 7-8 weeks out west. We are from Indiana(flatlanders). Our tv is a 10 year old Diesel with 164k when we started. We now have 168k and are still 2k+ from home. Our traveling CGVW is about 19,500#. We have crossed the Rockies twice, once by interstate and once by 2 lane twisty US and State roads. We have also crossed the Cascades twice in the same fashion. I changed the oil and filters before we left and have now added any oil since. We have not seen any broke down trucks or MH of any kind along the side of the roads, even on the real long up hills with 3000' elevation changes. Out here fuel has cost on average a little less than $4.00 a gal. and I drop $100. about every 275 miles. In my case oil and air filters are less than $20. each and fuel a little more. I use Rotella T syn. oil that I buy at Wal-Mart at Less than $25. a gal. and I use 3 Gal. I do my own changes. My truck has had a water pump change,muffler and exhaust pipe change(they were not stainless steel) and front sway bar down links changed.On edit, I have had the trans rebuilt too at 154K. When not RVing the truck is my DD. I think for the price of a new one I can do a lot of up keep and parts replacement. It fits my needs. JMHO.