I read an article in a boating magazine back when gas was outrageous that talked about getting the best fuel economy while towing. One of the tips given was to keep the RPM's at or below 2000, towing or not. I've used that since I read it and have found that it seems to work quite well. I will say that keeping it under two grand while accelerating is painful and I rarely do it, two grand while cruising is easy and in the 4Runner that's just a bit over seventy miles per hour. I've used that two grand rule in multiple stock vehicles and they all vary on exactly how many mph that is but they all seem to get the best mileage if I stay with 2000 RPM while cruising.