Northwest Without jakes

Hey all just looking for advise. Recently bought a 1986 KW K100E Cabover aerodyne with a 3406C catapillar and a 15 speed overdrive. The engine doesn't have jakes on it. I've been trying to get them put in but every time I order parts cat calls and says I need more. It's basically come down to I have to drive this truck due to other truck needing work. I run Kansas city to Portland and back every week pulling a 53 reefer. Looking for advise on the mountains with no jakes. I'm 28 years old but have been driving since I could reach the pedals. But I've never had a truck with no jakes. I've got a n14 currently and with jakes I still have to run down cabbage and others in low side 5th gear since none of the n14s I've had seem to have had strong jakes. I'm assuming the cat will be similar but have heard so many different stories on how to do this. My father has been doing this 40 years and said to just take it low gear and slow with light steady pressure on brakes letting the motor/Trans and brakes work together. He's made a couple rounds in the truck before me doing this and everything seems to have gone fine. Just curious on other experienced drivers in this area of driving. I like to research the crap out of everything before trying it myself. Sorry for the long post and thank you for any advise on this it's greatly appreciated.