Gear choice

I installed an overdrive to cruise 65=2240. Much quieter, smoother, relaxing.
Before od my car was cooking 65=2870 (manual trans) and had an annoying sound at 65, notta boom, just "impatient" The body just amplified whatever the exhaust was doing.
But at 65=2240, that is gone; thank God.
My engine sounds really good at 2800, so that is my preferred shiftpoint, and I make the shift lazily. This gets me 63mph, then into od, and lets cruise.
The point is that I have a choice.
If you are limited, then just know that your 5.9 will cruise either; but always go for the lower of two choices. The 5.9M has a generous amount of bottom end torque, so 3.21s would be my choice. Allbeit; I would likely stall it at 2800or so, and run a lock-up.