I decided to read the owners manual about driving with a trailer and what gear to be in. I have been driving in D this year and I have had no hunting issues and the gas mileage is better. Upon reading the manual I found that it said that while towing you should dive in 4 not D for engine braking. It never mentions transmission issues as a reason to drive in 4 instead of D.. My truck and trailer brakes work very well and the 4.0 does not have enough compression to engine brake for me anyways.
Just my observations. I will continue to drive in D and if it does start to hunt I will down shift.
I think a clear idea of what hunting is is needed as well. Hunting is not your trans dropping into the passing gear while in drive and then back every once-in-a-while. Hunting is the trans going back and forth from gear to gear in rapid succession say 5-10 seconds apart. I have never had the Taco hunt I only give it a little help getting into a climbing gear either 4 or 3 before the trans does it for me.