I think with the reduction in RPM I will be able to cruise 65 and still get the same mileage.
@ 65 with a 13 speed I'll be turning 2300 RPM, so 500 less than I turn at 55 MPH right now.
regardless, I'd take a 2 MPG hit in mileage to do 65-70. 55 MPH brings the full suck. It made our trip to Harlan last year a 10 hour drive. I did it in 7 and a half with truck and trailer.
well I don't have many other options. unless you can find me a 4.33 third member for a Spicer F155-S axle. I've pretty much exhausted all options.
If I lack the power to turn it in double over I can drop to single over, run it on the governor some more and start finding bits to put a turbo on it.