Yep, you gotta love the Tow Haul. Another reason to use it often, even on seemingly slight grades, is to reduce your transmission temps. By engaging the TH you can reduce your trans fluid temps by as much as 10 degrees as it will not only be working more efficiently (for the load on it), it will be cooling more efficiently.
Just another very good reason to get a Scan Gauge or similar display. Being able to see a digital read out of trans and coolant temps is a real eye opener. Ford "gauges" aren't really gauges. The display leaps up to the mid point and stays there until until excessively high then moves quickly to the max. I have seen 224 degrees of coolant temp while the gauge had not moved from the midpoint and not many, if any, fords I have seen come with a display for trans fluid temp despite the ECM having that data available through the OBD port.
On long down hills the TH really shines. I can run down a 12 mile 6% grade with the TH engaged and virtually never have to touch the brake pedal. It will hold me at 50-55 in fourth gear and a single tap of the brake pedal will drop it down in to third for increased braking (control) should the grade get steeper. The best part is you are not burning a drop of fuel all the way to the bottom. If you don't have TH you can get similar results by locking out O/D.
Works for me.
:B