For general use (not drag racing), and occasional towing, I would use something in the 1800 rpm range max.... the torque of the engine setup will make a low stall convertor work, and much higher and you will be spinning more RPM's as you move out for no good reason. The 4.10 will do a lot for any towing. My '07 Ram Crew Cab with CTD stalls in the upper teens range, and I tow with it a fair amount.