I recently had surging problems and soon after a real lack of power and no smoke even with the DDUFM set on 5x5 on inclines up to and greater than 6% pulling a 10k load although it still manged to pass a Duramax . I had checked everything I could think of and called Fred at Desert Diesel parts to discuss the problem and solution. Fred recommended sending the box back. Shipped it out on a Saturday 2nd day air and received a new box on the next Friday. "GREAT CUSTOMER SERVICE" from the people involved. Box is installed and runs great.
Dave
Dave