If you’re really tuned into your truck, you can see what’s going on with the transmission by watching the tachometer. There will be a slight but noticeable increase in rpm when the torque converter unlocks and a couple hundred rpm increase with a downshift. There is likely not much of a mpg change using 6th, nor increased engine wear. It takes a certain horsepower (either fewer larger explosions or more smaller explosions) to overcome friction whether the engine is spinning at 1500 or 1800 rpm. I say let it spin freely and use lower gears when towing or working hard.So from your experience towing my 2400 pound bass boat on the highway with a 2019LC, stock gears, 33's, lift...I should stick to 6th gear? I have towed in 8 for a couple years, never more than 100 miles at a time.