I like my 2002 3500 QC SLT 4x4 Dually and take it of-road in deep sand on beach and will occasionally tow a race car and a trailer but I have not put the engine under any load- Cummins says 10-20k but seems to imply that a "good" break-in needs the engine to be loaded- I just like diesels and hope that the motor doesn't need frequent loads to be happy- I have 5200 miles on it- took delivery in late December- mpg is combined 14-14. 5 and 17-19 on a straight highway run at 65-70- I have 4. 10 rear locker- Dana 80- does everybody out there tow with these?