In regards to exhaust brakes...I have a rig with the gas V10, and a diesel with an exhaust brake. Coming down a mountain pass with a load with the gas engine, yes, it downshifts but seems to hardly hold back the load at all as the tach zooms up to 5000 rpm. Eventually I have to use my brakes because it just keeps accelerating. With the same load behind the diesel coming off the same pass, once I engage the exhaust brake I don't have to touch the brakes. Matter of fact, I generally have to disengage the exhaust brake (mine is manual) periodically because it slows me down too much. There is simply no comparison in hold back power.
