I drove a 3.31 unit before driving a 3.73 and I noticed no big difference on the std length units. On my old EL with 3.73s I did notice 1st gear was pretty much useless in DD. I would be out of first gear from a stop and into 2nd before my back tires even crossed the white stop line.

The best money you can spend since your are ordering is the rear air suspension. I've had it on my work one and my current King Ranch and it makes a noticeable difference when loaded.

The 3.73s feel about the same on my 2013. The best $$$$ spent isn't the 3.73s which will feel much deeper than your current 3.73s due to the extra cogs.

Your old 05 was a 4 speed the new 6 speed adds two cogs.

3.31 or 3.73

1 2 3 4 5 6 R
4.17 2.34 1.52 1.14 0.86 0.69 3.40

Old Trans:

1 2 3 4
2.71 1.54 1.00 0.71

So if you look your list gear with 3.31s is deeper 13.80 vs 10.11 so your engine is turning over 30% faster at the same given RPM with a lower final ratio. People today get too hung up on finals without looking at gear spread and what we in the industry call gradability. A 3.31 equipped 6 speed expedition will out perform a 4 speed 3.73 all day every day.

Hopefully the above ratio and gradability speak makes sense.