Duramaxs around me in the asking price range of $20k have almost 200k miles or are just pos trucks all beat up. That truck with a duramax and that low of miles would be $25k plus and they couldnt keep them on the lot for that.
The 6.0s are great motors, we have had several. Its just not a diesel. I wanted a duramax but found an 04 3/4 ton crew cab 4x4 cummins with less than 100k miles, had new front leveling kit, new tires, aftermarket rims, hard bed cover, spray in bed liner, lots more. Gave $18k for it. Sold it last year because I started a new job and was carpooling with the wife, she cant drive a standard so we were always taking her car. The dodge was getting 20-22 mpg but cost over $100 to fill it up and would go through a tank in a week just driving back and forth to work. Her car only cost $50-60 to fill and would last a week also. So the dodge just set, I still had a monthly payment on it and insurance so it just wasnt cost effective for it to be setting. So we sold it. Regret that decision almost everyday since. Towing with a gas vehicle just isnt the same.