The pre DEF/emissions diesels are very sought after right now. Not surprising at all that yall's mid 2000's Cummins trucks w/ low miles sell like hot cakes and still bring good money. I couldn't find one I was happy w/ when I was looking a couple years ago. Forget a mega cab...those things must be gold plated, lol.
I ended up buying a 2006 Duramax and have had more people ask if it was for sale than I ever expected. Even the '01 Cummins I had before sold in less than 24 hours on Craigslist for $1k less than I paid for it 7 years earlier.

If all I had was an open car trailer, I'd just have a gas truck to pull it with. An enclosed trailer is a whole different ballgame...I much prefer the power of a diesel for that.