We are very happy with our 2013 3500. We went for the Laramie because we plan on keeping this truck for a long time and felt we wanted all the bells and whistles. Plus the cost difference from the lower trims to the Laramie was not that significant when the total cost was factored in. Ours has 3.73 gears with the G56 manual which pulls extremely well. I too am confident that the 3.42 gears would be just fine because the Cummins has so much low end torque. In fact, lower RPM's at highway speed would be welcomed by me! If I were ordering a new truck I would seriously consider the 3.42 gears.
Your payments that you quoted are very reasonable. Unfortunately mine are considerably more than that and for a longer period! At least I got a very good interest rate and can pay it down quicker if I choose to. I have no regrets buying it because I know it is a good investment in our future for many years to come.
Oh, and ours does have the single CD option which is located in the centre seat lower storage area. We have used it, but admittedly we usually use the satellite radio anyway.