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Message: [QUOTE="me2, post: 384317, member: 3825"] 8-8.5 MPG is what I am seeing, under very good conditions. I am generally driving less than 64 MPH. It doesn't seem to get better even at 60 MPH. Its hard to drive 60 MPH when you are going 400 miles. Its totally stock. 10+. I don't think my F250 (5.9CR, ZF6) ever really got less than 10 MPG pulling this trailer. I don't really consider this a big, big trailer. There are lots that are bigger than mine. The high end 5ers are all 2-3000 pounds heavier than mine and then there are the triple axle toy haulers. My approach is to build a torque monster engine and use the 1st OD gear on the 6R140. My 20 inch tires are 605 revs per mile or thereabouts. 605 revs per mile x 3.73 x 0.86 = 1950 RPM at 60 MPH, 2100 at 65 MPH and 2260 at 70 MPH. Lets say the engine is making 1000 ft/bs. At 60 MPH, 1000 x 1950RPM / 5252 = 371 HP. At 65 MPH, 1000 x 2100 / 5252 = 399 HP. That should be more than enough HP at cruise and the RPMs are right in the sweet spot as far as I am concerned. The only transmissions that I could find that have this sort of overdrive gearing are the 6R140 and the 68RFE. By comparison, with a ZF6, 4R100, 5R110, the Allisons, etc, all have OD at about 0.71 and the next gear under it is direct. (1.0) In OD (0.71) at 60 MPH you have 605 x 3.73 x 0.71 = 1602 RPM. Which is lugging for most engines. In direct you have 605 x 3.73 = 2250 at 60 MPH, 2444 RPM at 65 MPH and 2632 RPM at 79 MPH. 2250 at 60 MPH is OK, but the rest is a bit fast for me. Fuel consumption seems to go up a lot at higher RPMs, loaded or unloaded. 4.10s and smaller tires change all these numbers, but the better they make them for towing in OD, the worse they make them for running empty, which I also do a lot of. The real issue here is the gear spread from the top OD gear to direct and the lack of torquey engines. On the 6R140 the ratios are 0.67, 0.86 and 1.15. The 68RFE has even better ratios. All the rest of the transmissions out there have a big gap between OD and direct. And no stock engine is making 1000+ ftlbs. The right engine coupled with the right transmission will make towing these big trailers very easy. [/QUOTE]