It didn't make any difference in my case. I'm still confused about the operation of the brake.
I come off a ramp from a downhill freeway at 60+ mph in Tow/Haul and Manual Exhaust Brake mode. Using just touches on the brake pedal, the exhaust brake will engage through every gear all the way down to 2nd, and release at about 20mph in second gear. I use the brake pedal to come to a stop at the light. This is the kind of operation I would expect from the brake. I then let my foot off the brake and give just a touch on the throttle (it's still down hill) to turn right down a short, steep grade with a speed limit of 35mph. I don't speed here because there's a light at the bottom of the hill. Even if I manually hold the truck in second with the button, it will roll right through 20mph and keep accelerating with only the compression of the engine to help slow the truck, no Exhaust Brake at all.
I now have a CTS gauge installed and the VGT parameter (which seems to go to 100% when the exhaust brake is operating - I guess it reads percent-closed) stays up in the 40% range (40% closed) in this circumstance. In other words, it's still positioned to provide boost, not braking.
To my thinking, in the "Manual Exhaust Brake" mode, the vanes should stay 100% closed unless I step on the accelerator. Right?
I assume the "Auto Exhaust Brake" mode should vary the pitch of the blades between partially open and fully closed as necessary to hold the truck's speed constant, even downshifting to produce more braking force if the fully-closed vanes alone won't hold the requested speed. Right?
Maybe Bob4x4 or Sag2 can let me know if I am assessing the function of the VGT correctly...