01-02 are the best years, check to see if the injectors were changed or have had maintenance on them. I blew up 2 common rail Cummins engines due to injector neglect. Have the rear end and trans checked as the Cummins engine puts out enough torque to make those parts the weak point. If an automatic check the overdrive out, if a 4x4 check the transfer case and have a good look at the fluid in it.