Gesus, not this again. :R One more time...........
The OP wants to go faster up hill. That takes more HP. Gears don't give you more HP; only more torque and torque is not HP. If all he needed more torque to the wheels all he has to do is drop a gear. But as Grit points out, this will slow him down even further.
Couple that with the fact that the OP does not like to go above 4,000 RPM but wants to climb hills at a high speed.
To climb that hill at the fastest speed the OP is going to have to hold that V10 to as close to 4,750 as possible. He doesn't seem to want to do this so there is no solution to this problem unless he wants to buy a new diesel. Then he can pull a mountain at high speed and make maximum HP at under 4K RPM and get 30% better mileage while doing so.