5-Star's tuning does not effect the functionality of your RV's tow-haul mode. That being said, since 5-Star's tuning already adjusts your Motorhome's shift points and pressures, you may find that you don't need to use the built-in Tow-Haul mode. All PCM tuning carries the risk of discovery by Ford Service Centers, which can result in powertrain-related repairs to not be covered under the terms of your factory Powertrain Warranty.