Just take your V-10 off of cruise whenever there is any significant grade and presto, problem solved, for free. Cruise is a convenience, an indulgence, but hardly a necessity. I would rather let my right foot make the decisions and reading the transmission fluid temps off of the Scan Gauge will tell you when it is time to engage the Tow Haul mode so as to keep the Torque converter locked up and give you optimum performance in terms of both mileage and power.
Lots of folks (like the OP), seek more performance from their V-10's when it it is there all along simply waiting to be tapped. Got a large grade to climb (?) put your foot down and go. Running a V-10 at 4 or even 5,000 RPM is not going to hurt anything but your mileage. Max torque (happily), comes along at around 3,200 and max HP at closer to 4,500 so where is the problem???
If you bought anything with a V-10 expecting "good" (?) mileage the error is yours, that is not what they do. If you want the power they possess all you have to do is use it, the choice is yours.
:C
