I know the accepted way to use brakes on a hill is to stab them, and then let it run, and stab them again. And I wasn't going to say anything. But having driven 18 wheelers without Exhaust brakes. I have a little experience.
The first time I started down the mountain I did as y'all say. Slowed it down, and let it run, slowed it down, Y'all remember, a diesel with out a add on exhaust, or engine brake has no braking on it's own. It just free wheels in any gear. Any way. The trailertruck driver of 28 years, next to me in the truck, Asked me a scary question. He just looked over, and said. Which one of the runoff ramps are you going to use? I said HUH? He told me, If I kept doing it the way I was. Letting it run, and slowing it down, I would have no brakes before I got half way down. He told me to hold it at 35 MPH, no faster, no slower, steady pressure, and it would do what it was supposed to do. My way would smoke the brakes. So I did it his way, after all, he had more safety awards than I had years. When I got to the bottom, There was no smoke, no smell, no fade. So I do it his way. You do it how ever you want.
Now with the gas truck. I have all the engine braking I need, If I had a diesel. It would have a jake. IMOP they should be required on all diesels.
Now for the OP this is a mute point. He has a gas truck. All he needs to do is drop to 1st, and let the engine hold him back. If it holds back too much, go to 2nd. He shouldn't have to use his brakes much at all.