Diesel Sprinter downshifting to slow question ?

For the T1N1 5 cylinder diesel on my rv I often keep the txn out of 5th and in 4th on steep winding roads, downshifting to 3rd as needed. I keep revs below 3500 and more like 3000 for the 5 cylinder. Compression braking isn't a big benefit. Sprinter brakes on mine are quite good and don't fade much even under heavy use, which is seldom. It is essentially a truck so I drive it like one, including downshifting out of o/d 5th on steep incline hills.