I can't detect any difference with the engine brake/tow-haul mode on or off. The downhill downshift (or whatever it's called) seems to do exactly the same thing. I don't detect any difference between the shift points (RPM) either. There's supposed to be an exhaust brake. While I don't expect it to sound like a Jake Brake, I hear nothing. I was towing 4,000 lbs BTW. What's your experience?