Out west here we have plenty of steep grades to test out your motor, with my 06 PT/C13/525 the max torque is around 1500 rpm, 49 psi boost, it will pull down to around that rpm and really go to work, just have to watch the temp gauges. Most all grades it will pull in 4th gear depending on the outside temp, I've run the temp up to 205 and then shift down and cool the motor off, my fan shifts to high speed around 196 degrees, i can hear it when it shifts. One thing to note I clean out the radiators every year so there is no crap blocking the air from passing through them.
All so the altitude will make a big difference in you motor performance the higher you go the thinner the air, pulling I-70 in Co your lucky to get 40 psi boost.