I have a chevy c4500 with the duramax engine and allison transmission.
I leave my exhaust brake on all of the time, even when not towing. To me it adds a little bit of extra safety. I can let off the throttle and the truck begins to slow quite a bit. Almost to the point where I don't have to use the brakes.
Try it you'll like it. I tow a 15000 lb 5th wheel and the exhaust brake will hold the speed downhill at 55 MPH on a 6% grade... I never have to touch the brakes.
One tip- the exhaust brake and the cruise control don't always see eye to eye when going up or down a big grade. I turn off the cruise control when I begin to climb or start down a grade.