That was ONE of the best mods I did to my '07, 5.9 besides the free spin hubs. In 2008, my wife, myself and out two grown daughters traveled to Yellowstone towing about 8,000 pound Travel Trailer. Coming home on I-80 WEST from the Donner Summit all the way down to Sacramento, I NEVER touched the service brake. 6th and 5th gear with the PRXB Pac brake did the whole job of keeping us at a safe downhill speed.