Just back from trip to Florida tow show. 18.4 MPG over 2300 miles, about 8000#, mostly 68 to 74 MPH some up to 80 MPH. What could I expect with a 6th gear???? half, 3/4, 1 MPG better???? Those who have enabled the sixth gear care to chime in, Thank you! Is it worth the expense? What is the least expensive way to enable the sixth gear? (04.5 LLY) How strong is the sixth gear, for trailer pulling, can it be locked out so fifth is top gear when pulling a heavy trailer? Thank you. bob.........................