Engine Brake - not much difference on/off

the truck has a variable vain turbo (excuse my spelling if its wrong). down shifting manually and when the truck does it on its own are very different. if you downshift, it is strictly the engine slowing the truck, but if it is in tow haul, the turbo will create back pressure which will be like an engine brake on steroids. may be hard to notice at times but if you try both while going on a slight decline, you will notice a pretty big difference.
also, if you have a lead foot, you will likely never notice a difference in the shift points. take the truck out in tow/haul and get it up to 60-65mph. then turn the tow/haul off, you will notice that the truck wont go into 6th gear while tow/haul is on until you get to a pretty high speed (70+)
hope i helped

That is helpful. thanks.

The engine brake is computerized... downshifting doesn't seems to get it to kick in, it's the brakes that seem to trigger it. Just make sure you're in tow mode and hold the brakes a bit at highway speed. It should be very obvious that it's engaging. It can get embarrassingly loud when stopping a 6500 lb boat.

I noticed that just letting off of the accelerator while on a rather curvy county highway at about 50-55 mph, not sure what gear it was or how high my rpm's were (I figure they were kind of higher as, like you said, the higher the rpms, the more you can tell it is working), but I could tell it was working to slow me and my 12x6 trailer with 2 atv's down.