With trucks the Range mode shuts off the downhill grade control completely which is not good when towing. The tow haul mode is designed to protect the transmission when towing a very heavy load. With trucks that is 75% of the maximum tow load per GM's recommendations. On steep 8% grades I use tow haul with any load as it makes for an easier descent with very little use of the brakes needed.
Range mode puts your vehicle back 20 years in towing performance. The only time it is advantageous is when starting out on soft ground where you can shift it into 2 gear and the vehicle will apply less torque to the rear wheels to minimize loss of traction.
