There's a tremenduous forward-bias weight penalty to pay just to get some lower RPM quietness when trying to tow with a diesel pickup. That's probably one reason why so many diesel pickups are 4X4, because when unloaded in the rear they must really suffer from poor rear traction in slippery conditions.
Regarding diesel exhaust braking as compared to gasser geared-down braking - the 4:56 differential gearing of our 12,000 lb. gas RV's truck chassis provides way more hold-back in the lower tranny gears than we've ever found necessary for downhill braking.
