Downshifting when going downhill question

[CRV2]

I don't think that there is a truck or motorhome that has an engine with enough compression to be useful for braking purposes without downshifting into a lower gear (at least not on a ~6% grade). Trying to spin an engine ~5000 rpm provides significant braking, in fact when I downshift (or let the E450 do it on its own) rarely is ~4000 rpm needed to keep from gaining mph.

Point being, if you aren't getting enough braking to keep from gaining speed, then you are going to fast and in to high of a gear. ~CA