I really don't see why you're trying to reinvent the wheel. The additional parasitic drain from the alternator will negate any power gain from getting rid of the mechanical fan.

1. The mech fan was designed to work for your motor. The only time it has let you down is because it got tangled in a wire.
2. The money you'll end up spending because of relays and thermostatic controllers for your fan will make the fans just as expensive.
3. How often do you make water crossings deep enough to hit the fan?
4. Will the electric fans cover the whole radiator or are you going to have to make a massive shroud that will take up as much space as the mech fan?

I'm not trying to be a dick, but stop trying to reinvent the wheel. What's wrong with the mech fan? Maybe there's a reason you can't find anyone who has put electric fans on that truck?