Hmm so u have actually ran ur engine to 4000rpm to hit 70 I feel like she would be be literally anialating the fuel at that rpm lol and would over heat am I jus trying baby my engine haha cuz I try not to run it over 3000 rpm and had sum overheating issues fully loaded doing 50mph at 3k rpm
yes, 4200 RPM to hit 70mph. I get between 8 and 9mpg, depends on the kind of driving I am doing. I think 60 sucks less than 70! (weighs almost 9K empty). I pulled my 35' travel trailer a to a vintage trailer rally in September (fairly flat, just up I-5) and got 7.9 mpg. I kept it around 60 with the trailer on. (trailer weighs a little over 6K).
If you put a 2-speed rear in it, it gives you more gears but no more top end. You would have to go with an overdrive, different rear end ratio, or taller tires to get more speed. The latter 2 may make you unhappy pulling any weight as you may have fun getting it rolling and then not be able to find the right gear pulling a hill, even a slight one!
As stated before, clean your cooling system out real well (have your radiator rodded out, or replace it) and you should be fine running 60 MPH.
