I'll chime in on a little new truck BS.
Nonesuch,
I get about the same as you. 15-16 in town, 17 towing in direct drive, and I get about 22 on the highway at 70. I am turning about 100 RPM's less than you since I have the 3.54's.
Tim,
You will like the new truck, One of my favorite things about eh 3rd gen cummins trucks is the fold out towing mirrors. That is the best mirror design I think I have ever seen on a pickup. They look very good folded in and are plenty large enough to actually be usefull(unlike the late 90's chevies). THey look very nice and "beefy" too. The nice part about them on the 3rd gens is they are power mirrors, with the 2nd gens like mine they were an option but non power, only the smaller mirrors were power(which is what I have). I also like the look of the short box crew cabs, the SB quad cab 2nd gens are a little too short for my taste. The 3rd gen back seat and door seems to add just enough wheel base. I am still not sure if I like my front clip or the new front clip better, regardless they both have to be the sport version for me, I don't like the big chrome front ends. You will like the NV5600, it shifts smooth, tight, and fast for what it is. It feels like a lot tighter box than the nv4500 in our C30 Chevy dually. THe gears are really close together. When I test drove an '03 I stuffed it in 4th instead of going into second the first couple of times because I was used to the 4500 and the gears being farther apart.
I am disapointed with a couple of things:
1) I don't like the interior in the 3rd gens, the white guages are cool but I really like my interior in my 2nd gen '01.5 a lot better.
2. I am not sure if it's a good thing or not that the new rigs have AAM axles instead of Dana axles.
3) THE QUIET CUMMINS! I am definantly not a fan of that multi stage injection deal at idle to reduce noise. I like it when I pull up to a Ford or CHevy diesel and all they can hear is cummins next to them.

The cummins has that legendary sound, It is fairly loud but it does sound a lot better than the PS or DMax IMHO.