You will see some benefit in the manual climbing since you aren't spending power making transmission fluid nearly as hot in a manual as you are in an auto. However, miracles should be not be expected.
Here is a perspective. With my 60 heavily loaded drivng from San Diego to Bishop and back, pulling my off road trailer, reach 4000' altitudes on road (hit 10.5k' off road), it's still slow. I can usually pull grades at 50 MPH in 3rd or even 55MPH (for comparison, the 2F wouldn't have pulled more than 45 MPH) if I want to hold the engine at 4k RPM but other vehicles are still passing me (or me pulling over to yield). Acceleration off the line is very poor compared to say my buddy's FJ Cruiser that was equally loaded down. It is possible that having a 3rd gear in between your 2nd and 3rd will also let you reach the 50-55MPH range. At the end of the day the 3FE is a 155 HP engine where modern equivalents have at least 100 HP more. On those CO grades in the higher elevations the 3FE powering anything is going to suffer unless you turbo it.
At sea level it is quite livable though H55F just made it all that much better.
Frank
Here is a perspective. With my 60 heavily loaded drivng from San Diego to Bishop and back, pulling my off road trailer, reach 4000' altitudes on road (hit 10.5k' off road), it's still slow. I can usually pull grades at 50 MPH in 3rd or even 55MPH (for comparison, the 2F wouldn't have pulled more than 45 MPH) if I want to hold the engine at 4k RPM but other vehicles are still passing me (or me pulling over to yield). Acceleration off the line is very poor compared to say my buddy's FJ Cruiser that was equally loaded down. It is possible that having a 3rd gear in between your 2nd and 3rd will also let you reach the 50-55MPH range. At the end of the day the 3FE is a 155 HP engine where modern equivalents have at least 100 HP more. On those CO grades in the higher elevations the 3FE powering anything is going to suffer unless you turbo it.
At sea level it is quite livable though H55F just made it all that much better.
Frank