built in trailer brake controller

I have almost the same truck and my trailer brakes work like they should with or without the tow/haul on.

I have an '09 and my brakes worked normal with tow/haul on or off.

You sure it's not other factors in the tow-haul mode making it SEEM like the trailer brakes are working better? Doesn't the Allison transmission downshift as you brake while in tow-haul mode, giving you some engine braking? I know mine does to a degree, and it's a much older model.

The tow/haul has absolutely no effect upon the braking system. It only controls the shift pattern of the transmission.

I just traded a 2008 Duramax/Allison (100,000 miles, mostly towing) on a 2017 similar model. My integrated brake controller did NOT work on the disc brakes (electric over hydraulics). It was an easy fix. Just had to wire in two (one would probably have done) brake magnets between the brake wire and the actuator. It then worked perfectly. All this relates only to install of disc brakes. The IBC worked perfectly with the original brake system.

Again, the tow/haul has no effect on the brake system, but it sure does help to keep the speed down on pass descents and in that way surely helps to keep from using the brakes too much.

NJRVer wrote:
I have an '09 and my brakes worked normal with tow/haul on or off.

^^^^ this x2.

The downshifting and "slower" shift points in Tow/Haul mode noticeably improve the authority of starting and stopping my 2009 2500.....if the trailer brakes seem better with Tow/haul on, I'd estimate that it's the general improvement of Tow / Haul being on, not any effect on the trailer brakes.

Tow/haul has no effect on the trailer brakes directly. I suspect that the brake control has a momentum sensor. When using tow/haul the automatic downshifting makes your truck decelerator harder. This could possibly make the trailer brakes be applied harder.
However, I've never noticed this phenomenon in my 2015 Chevy. The trailer brakes work the same tow/haul or not.

Thank you for all those that replied to my query. I guess my problem may be in the trailer or controller itself.
Wayne