I use the tow/haul all the time...very rarely turn it off.
These rigs are almost loaded out to the max, so you are almost always "hauling" in addition to towing.
Others will argue or have their own opinion, but it's best for you to experiment and find whats comfortable for you.
Same goes with the cruise control. I have found with the 5 Star, the cruise control , on slight grades, keeps up, and only drops off on larger grades. If its pegged at 65 mph, at the top of an overpass type grade on an x-way, it might drop off to 62-63, but I'll still be in overdrive, rather then the tranny dropping to "screaming 3rd" to maintain speed.
Go to IRV2 web site, under Vendors Deals forum and you'll find hundreds of posts about the 5 Star tune.