This is posted on the official site.

"Though we do now have some nice special guests lined up. One who appeared at Truck 2000 and one who appeared at Truck 2002."

Here is the 2000 line up:
http://www.truckfestival.org/history/truck-2000

Here is the 2002 line up:
http://www.truckfestival.org/history/truck-2002

So, ladies and gentlemen of DIS, scartch those beards and think, hu could the guests be