I would say that most of the time, I leave it in T/H mode. I like the firmer shifts and the early TC lock-up. Firme shift + early TC lock up = less heat and wear. <---- to me anyways.

 

after getting up to speed,say 60 mph w/15000 lb 5th wheel in tow haul mode is it ok to turn it off so rpm will drop=better gas milage/temps

 

Leave it in Tow/Haul mode, as it will not drop your RPM's any lower going back to OD. Tow/Haul is the same, as OD except your shifts are a bit longer and firmer and it will also down shift to help you stop better. Towing 15K and it having to shift into OD Off ( before it goes back in to OD) will raise your RPM's very high and my self I don't like to see my engine rev past 2800 RPM's to get it back into OD when it is perfectly fine to run it all day long in Tow/Haul mode.