Well, in fact it is possible to lug an automatic. If you've done like I have and upgraded your auto trans to fully built, billet-everything bulletproof specs which includes the ability to manually lock the torque converter, it is possible to lug it.
Also, if your '02 Cummins hasn't got enough power, you don't need a whole new truck.
Do a few simple things like installing a wire-tap tuner and bigger injectors and it will run right with the new ones. The basic engine in your truck is just as stout as any. It's all about the fuel system.
If you have a Cummins and you want more power, it's there for the taking.