There are all sorts of machining and re-machining strategies that might help, depending on the specifics of the surface you're trying to produce. Parallel passes generally work pretty well on areas that aren't too steep, but as you get over about 30 degrees of slope, you start noticing that the passes are further apart, and the cusps are getting larger. If these are fairly large areas, say a central "plateau" with steep sides, you might isolate the plateau as a separate area and treat the sides differently, for instance with a waterline strategy that spaces the passes no more than a certain amount apart vertically. But sometimes the steep area is comparatively small; in that case you might want to isolate it with some curves, and use a "between curves" machining strategy.
Sometimes it makes more sense to machine the whole part one way, then look for the places where it didn't work too well and use a different strategy with them on a subsequent series of operations that smooth over the rough places, perhaps with a different tool that better gets into areas of high detail. All this can end up taking more time, either in the CAM programming, the machining time, or both. But if the part demands it, you may need to do it anyway.