I tow a 4500lb camper while running 285/70R18 with stock gears on a chunky, scratch that, FAT cruiser. Most of the time it’s totally fine. However, Colorado mountain passes were sucky. Just as
@TeCKis300 explained, there is a torque hole and it can be unnerving on long climbs or descents if you aren’t thinking ahead and preparing for the climb or descent. You will definitely need a scan tool to watch extra gauges, trans pan, trans torque converter, gear selectio, and torque converter at minimum.
My MPG sucks when not towing so it’s not much worse when towing, I would recommend you don’t even consider this data point as it’s irrelevant and unchangeable.
I have the 8 speed and it doesn’t hunt because I’m its boss and tell it what gear we need when we get into the hills. Otherwise it’s in 6, which it’s always in 6 regardless if I’m towing or not, and it gets to think for itself.
One of these days I’ll re-gear and probably do 3.90 or 4.30. Fantasy land would be super charger but idk if that would ever happen because our build purpose is dragging our camper off road and the extra 100 ponies under the hood wouldn’t benefit me there, plus there’s still no ECU tuning possible.
If you run trails and wheel off road then get the tires. Embrace the money pit and enjoy.