Sounds about right to me.. Anything past that falls into the realm of diminishing returns for the fuel it costs verses the few extra foot pounds of torque you gain.

I'm back to my old driving habbits again and I do tend to shift at around this RPM, and run just under that in the 1400 range (probably closer to 60 - 70% of peak torque - but acceptable with lower resistance).

As a lot of others have pointed out, it does really come down to feel, and it is very much like riding a 10-speed bike. I think the 4.0 L in the 2nd Gen is more than robust enough to handle the lower end and is a prefect fit given the size and weight of this truck.