Best Way To Maximize Fuel Mileage Going Up Steep Grades?

When I started driving it was a 1966 kenworth with a 5 and 4 speed. 262 hp was under the doghouse. Then went another cabover with a 318 detroit. You know 8 V 71. I doubt most drivers know what that is. Then an old matlock truck with 3406 A model with spray nozzles instead of injectors. Also it had a ten speed, mo more twin sticks for me. Then my dad past away and I had to buy a truck or lose all of his accounts. So I bought a t600 kenworth. Cunmmins n14 red top, great engine no problems in. 6 years. well that's my story but I did try to haul beer, I say try cause the beer was53000. Pounds so every load had to be just right. San bernardino to fresno everyday with the truck governed at 54.6 . Talk about long days. I retired shortly thereafter. So I drove from the time I was 18 to the time I was 50. Totally different drivers out there. Cowboys with one boot on, I call them.

Peak torque is between 1350 and 1700 rpms

Actually peak torque is considerably lower than that. Normally it's around 1100 RPM. Peak horsepower is higher in the RPM range.

There isn't much you can do about fuel mileage when going up a hill. It's going to take everything that truck has to pull heavy loads up a mountain. You'll keep it floored in whatever gear you're in. You could pick a really low gear that will allow it to climb the mountain half throttle but you'll be doing 15 mph. It's really not practical.

Yep, mash on it.