Moses,
Thanks for the info. I have counted the teeth on ring and pinion sets many times to determine ratios. Mostly for race car applications when the gear set is on the bench and not yet installed in the vehicle. I will attempt the drive shaft rotation procedure you described. I will also use a stopwatch and the mile markers to ensure the speedometer is accurate. My tires are Cooper brand and what is printed on the door sticker matches what is printed on the tire. Since I use this vehicle almost exclusively for towing, I suppose that 4.10 gears may not be the worst thing for my particular application. I considered taller tires the next time I replace them, but that may not be the best choice. I have yet to watch the video, but it sounds like that "tune" may be the way to go. I was just curious after reading your information regarding RPM and fuel mileage. I'll keep you posted.
P.S. I plan to tow the trailer at 65 MPH, which, as you noted above, puts me in the 2100 RPM range.