As demonstrated on here a bit ago someone sold a low mile truck on here that then appeared on eBay. It then went for major money. eBay has Roadloans and other financing available as well as standard credit unions the buyer can use on their own.
You reach a large audience with eBay for a flat fee. Someone wants a low mile Cummins may have cash in hand and book value can go out the window.
Have the truck detailed. Then take a picture of all 4 sides of it, bed, open doors and then picture it again shooting into the open doors. Picture of driver's side seat bottom that is known to wear, picture of odometer, interior condition, dash, and last 3 pictures of the engine bay. Optional picture of the underside and showing tire tread. Don't be afraid to take a picture of rust, dents, or defects. The buyer isn't there and wants to see and decide if they care about the issues - it makes them feel you are being honest with them.
List maintenance and other things you did to show you cared for the truck. This can't be found at a dealer or corner vehicle flipper.
List the truck to end on Friday and start the bid with what you want from it or a couple grand under that. Friday so the person can grab a plane or arrange shipping over the weekend. You may only get 1 bid so be mindful of that. Buy it now is nice, but, requires a reserve or it goes away at the first bid. Then buy it now it goes away after the reserve is met.
Offer to pickup at airport and finish the transaction at your bank. Hopefully open Saturday...
Last, don't be in a hurry. It may take a few tries/weeks to find a buyer. The value of a pre-emissions truck isn't going down very fast.
Edit: 140,000 miles is not "low mileage" to those looking for a low mile Cummins. This would be under 100K and the above example was like 35K. The miles on yours are average for the age at 15K per year. However when one looks at trucks for sale it is hard to find them with under 200K on them so no real argument - just helping you set your expectations. I don't think your price is out of line.