Just found out today, I believe three dsl classes.

 

There is a 2wd diesel, a stock diesel (no smoke) and an open diesel class.

 

In the 8,000lb open diesel class Paul Mcgrath took first in an '02 Duramax, Brian Randall took second in his '98.5 Dodge and Chris Muhs took third in his third gen Dodge. A F550 took the no smoke class but he was the guy that put up the prize money so the judges didn't seem to care that he smoked just as much as a couple of other trucks that beat him but got DQ'd due to smoke.