"does anyone ever use normal mode to pick up that 10th gear when highway towing?"
Absolutely not. The normal mode is all about mpg and nothing for towing nearly any amount of weight. You'll be engaging all those solenoids as the transmission hunts for the right gear, thereby decreasing the life of those components. In addition, the timing (ignition) strategy for normal versus tow mode is different. Normal mode has a slightly retarded ignition curve which actually reduces hp and efficiency under load, and in 10th gear, you have low oil pressure and high stress on the crank. Very bad combination for the main bearings.
When I tow, I lock out gears 8,9 and 10. My trailer is 6800 lbs and I found 62 mph is about 2400 rpm and I get the best mpg (10-11) and the motor is not working as hard, the transmission is not shifting so much, oil and water temps are stable (I have an OBD reader on my iPhone).
Even though these cars are very good at towing within their limits, if you are looking for economical towing, you have the wrong vehicle. One last comment - I changed my transmission fluid at 75,000 miles and the car effectively had about 20,000 miles of towing. The fluid was nearly black and there was the slightest amount of clutch material in that fluid. I changed the fluid, erased the adaptive learning tables, and it shifts as good as the day I bought it.