Tow Haul

Colo Native wrote:
Just wondering when to use Tow Haul? I know down hill is the best but any thoughts on the flat or uphill or just all the time?

Depends on the truck and tranny.
I've towed commercially over 800k miles in a 11 year period with LDT size trucks so I understand how to make a auto tranny last longer pulling 18k-20k GN trailers of various types.
The wifes '06 1500 chevy 4L60E tow/haul is worthless IMO. When pulling I simply don't use it as it keeps the TC clutch unlocked way too much at intermediate speeds especially down hill in 2nd gear. I find I can make it operate much more efficiently with less TC clutch slippage overall and much better down hill braking.
The '06 4L60E has no tap down feature for downhill braking. In fact with the TC unlocked in tow haul mode it has no engine braking. Might as well throw it in neutral and ride the brakes.

The 68RE/Allison and Fords big auto tranny T/H mode operate much different than our smaller sized auto transmissions.

Now having said all that many folks have no idea how to make a auto tranny operate for max longevity while towing or just around town so probably should stick with T/H mode.