engine brake while towing?

I do the same as coolbreeze. I think it depends on your particular truck and how it works. Tow haul on mine changes the programming on upshifts and I do use it when towing, except for descending hills. It is too aggressive when using the exhaust brake and downshifts when I don't want it to, resulting in me often having to add throttle to maintain speed. Yes you can use cruise control but I find I can do it smoother myself and don't like giving speed control to a computer when going down a 6% grade. A computer can't know what you want to do and it can't see ahead of your truck, it only reacts to the vehicle's speed. In aviation, it's called staying ahead of the aircraft. I find it much easier to just turn tow haul off when descending hills and do my own downshifting.

Everyone has to figure out what works best with their particular vehicle.