:)I own a 2008 quad cab, 4X4, SRW, 6. 7, 6 speed automatic with 4. 10 gears. I plan to replace my 35' 5TH wheel toy hauler with a bigger one with 3 slide outs that weighs about 16,500 pounds loaded and ready to go. Should I refrain form using 6TH gear? The truck has about 12,500 miles on it and...