Back off the throttle slightly as well on long steep hills so that the engine is able to accelerate a little and not working quite so hard, you will only lose two or three mph and the traffic behind can take care of itself. Downhill as said change down if long and steep, particularly so if the road leads into a built up area. As with all heavy vehicles the brake assistance pump needs to be kept turning quickly to cope with demand. Repeated frequent short bursts of braking at low engine rpm can leave you without brakes not just because the linings have got too hot. The modern car-aimer hasn't a clue why you are going so slowly so ignore him when he starts roaring past blowing the horn, unless you are sorely tempted to give him the finger.