This effective gear ratio that you mention, exactly what do you mean ??? On my old truck (2004 Nissan Titan with a 5 sp, it had a lower gear ratio of 3.357:1) with my new truck having a 6 sp transmission (3.42 gear ratio) I wonder what the lower gear ratio would be. My new truck comes with the HD Trailering equipment which includes an external transmission cooler. You mention 13 mpg towing on flat land (I'm assuming that measured using US gallons) - that would translate for me to around 16 mpg (Imperial gallons) which I would consider to be quite good. Another question - when my truck comes from the factory - do they put in synthetic fluids ???