Colleen,
Exhaust brakes (sometimes called engine retarder brakes because they work against the engine exhaust) are wonderful. We had a Pac Brake on our last motorhome and a Jake Brake on this one. There's usually some kind of a rocker switch where you can switch it from high to low, giving you two different levels of braking power for different steepness of grades. Used properly you sometimes can drive for hundreds of miles without ever using your service brakes. When you approach a freeway exit, use the exhaust brake to slow down and you won't need the service brakes until you're almost at the stop sign or turn. Ours "cuts out" at about 15 mph and you will feel it stop the retarding action when this happens. Practice using the exhaust brake on easy slopes so you feel comfortable using it when you get to the real mountains. Test how the high and low rocker switch makes it slow down on some grades but not others.
When you see special signs for truckers that tell them there's a brake check area, that's usually your clue to get ready for what is probably a long downhill. Out here in the west some of our grades are 10 or 15 miles long, so it's important to save your service brakes for real emergency stops. If the grade is over 5 percent or 6 percent, it will usually be on a sign that shows a truck going downhill. If it says the truck speed is 50 mph, then my speed is 50 mph. In other words, follow whatever directions the road builders provide to the truckers and you should be okay. Some signs are quite unique. For example, on I-80 going over the Sierra from Reno to Sacramento, we've always gotten a kick out of one of the signs that says "Let 'er drift" meaning there are no curves ahead so you don't need to worry so much about braking. There also are huge "Slow Down" signs and they mean exactly that because there may be a bridge and curve at the bottom of the grade. We have a few places on relatively short grades that are 20 mph zones, and it's usually a hill with a blind curve coming into a town or coming to a river crossing where there's an immediate turn on the other side. Susanville CA is an example of the former and Mexican Hat UT is an example of the latter. By the way, with regard to speed, we can keep it at slower speeds when we're not towing. The added weight of your toad means you may need the exhaust brake more often.
When using your exhause brake, your brake lights on both the RV and toad probably also will go on. It's nice to have someone behind you verify that they are coming on as they should. Someone who has never driven an RV may think you're riding your brakes all the way down the hill, but the truckers behind you will know the difference. If a truck is ahead of you and you see it's brake lights go on, the trucker probably knows the road and knows there's a curve coming for which he needs to slow down. By the way, I tend also to follow whichever lanes the truckers are in while gong through metropolitan areas because they often know which lanes are problematic in heavy traffic.
Also on downhills, keep an eye on your RPMs when using the exhaust brake. You don't want your RPMs to get too high. We try to keep ours between 2000 to 2200 revs but this can vary by coach. This is when you briefly apply the service brakes to further slow the coach as Ned mentioned previously. In addition, there will be speed points on steep grades at which your exhaust brake needs supplementing with the service brakes. Our current Jake Brake is at 35, 45, 55, 65 mph. If I'm trying to stay at a truck speed limit of 50, then I try to keep my speed under that 45 mph point so I don't start speeding up. If you let it go to 55, then you probably will have to use your service brakes to slow down and that's when they get hot.
Did you get your Mountain Directory Guide (East and West) yet? You'll find they're quite useful because they tell you which roads are narrow, curvy, steep, etc. There are maps for each state with a number for each one of the areas discussed. They're great in that respect because you can pinpoint the route you want to take quickly. They're worth every penny in my estimation.
Don't worry about the mountains. They're beautiful and we love 'em!
ArdraF