We have an '88 Model 15 Eagle with a 740 Allison, 6V92 and no jakes. It was formerly a 'hound, so it's geared pretty tall--it doesn't hit 4th gear until about 55 mph. The gearing is a bit important if you're trying to decide what gear (and subsequently speed) to head down the hill.
Typically, on an unfamiliar 6-8% grade, I'll hold it in 2nd gear, which will give me about 40 mph at max rpm. I'll usually start the hill about 30, let it gradually roll up to about 40, then brake until I'm down around 30 again.
My preferred method of brake application is to apply about 5 lbs of application pressure for about 5 seconds; that'll cover the slow down between 40 to 30 mph. If you have an application gauge, get a feel for a low application pressure. . .the brakes stay a bunch cooler at 5 lbs of pressure than they do at 15-20 pounds.
That's my humble opinion. . .drive safe!