A freind of mine has a TST box on a 600 automatic, the box performs great but anything above 3/3 setting it may be slipping the torque converter or transmission. When driving down the road at about 55 mph when he pushes the pedal down hard but not enough to kick it down a gear the turbo spools up and there is a good puff of black out the tailpipe and it sounds like the engine revs faster than the truck moves. I was wondweing if anyone else with a 600 auto had experienced the same thing.