Hmm...I never noticed this one either. Strange, I just replied to the same (I think) question for another guy up in the tranny forum this morning too.
I'm not aware of any manual hub conversions for the 97-03 IFS Fords either.
The ring-n-pinion shouldn't be turning if your front axle is unlocking properly...just the half-shafts and the spider gears inside the gear carrier. This won't make that much difference in power/mileage if you could trim that out of the equation.
Fill your axles with a good synthetic gear lube and call it good.
How is your truck geared and what size tires do you run? Most 4.6s that I've seen have pretty tall gears for the tires they're running...if you regear lower, you'll see more bottom end torque applied to the road.
You could always SAS the truck too.

Then you could run your choice of axle and lockout.