Well, that's gonna be part of the game with a gas powered vehicle.. They can make tons of power on their own... They just make it at the higher rpms..
My little 3.5 liter V6 has some 365 hp and 420 torque... The peak HP comes in around 5500, but the peak torque is right around 2500 rpms... That's what you need to get up those long grades.
The "rub" here is that it's got a twin turbo setup on it.. :)
There is a 'cost' to this however... It creates a TON of heat in a short period of time, so you just can't keep giving it the 'beans' without monitoring the coolant temps..
Once you get ver 10 psi boost, the temps spike pretty fast. 230* is about as much as I can take, and then I back off.
Yes, I slow down and that's fine with me.
Okay, so you don't go 70, but if you are going 50 up the grades, that's okay too.. At least for me.. :)
Anyway, if there was a magic device to just bolt on, meet California Emissions, then it would be a widely known and down process.. :)
Good luck!
Mitch