Almost all diesels have turbos, so they are far less affected by horsepower/torque loss at higher elevations than normally aspirated gassers (except the EcoBoost.)
As for engine braking on downslopes, that is what it is made for. I've been reading the Sprinter forums on and off, and I've read nothing about avoiding engine braking. Idling, yes (as newer Sprinters will get their DPF plugged to the tune of $3200 for a replacement), but not letting the engine do what it is designed to do.
The 2014 Sprinters are shipping next month, and they are a redesign, although not as big as the T1N->NCV3 jump. This should help with handling, horsepower, and other items. Rumor even has it that 2015 might bring 4x4 Sprinters to US shores, and a four wheel drive Sprinter with a diesel generator would be a boondocker's dream.