mr_andyj wrote:
Please ignor all the post that start off saying "just..." With towing you dont "just" do anything.
If you are driving flat ground then keeping it in D is fine, tow mode or not. Tow mode will change the shift points of the trans, and there is nothing different about how the engine runs, just the transmission. Trans will rev higher before upshifting is what you will notice.
Yes, very much DO shift the trans into a lower gear for those white-knuckle downhills. Use the engine to maintain slow speed, not the brakes. I assume you have a gas engine? diesel engines will have very little engine braking effect without a Jake brake or exhaust brake engaged.
Gas engines do have a lot of restriction when off the gas pedal and coasting, so is useful.
Now, what gear to be in depends on the speed you want to maintain, the grade and the weight of the trailer.
Without researching the info you did not give us on your specific transmission, lets just assume you have a 4 speed with overdrive (5 forward gears). 5th gear is the O/D and the highest gear. With O/D off the truck will not shift into anything higher than 4th gear, and coasting speeds will be slightly reduced. In 3rd gear the truck will not shift higher than 3rd gear (no 4th, no 5th) and downhill speeds can be greatly controlled until the grade gets steep or your speed need to be dropped way down for turns.
Don't wait until the revs are high before dropping down to 2nd gear (truck wont shift into 3rd, 4th, or 5th) as is harder for trans to shift down when rpm's are so high (high revs in 3rd means way higher revs in 2nd).
Whatever buttons or levers or trickery you need to do to put the trans in the appropiate gear needs to be well understood by you before heading out.
Start dropping to lower gears, one at a time, well before you think you need to. This is not the emergency plan or back-up plan. Lower gears is your first solution to long downhill grades.
Using the trans/engine to slow the vehicle will save your brakes. Brake fluid will boil quickly and your brakes will fade or fail if you rely on them to maintain speed. This is not a good feeling. After brakes fail the engine can maintain speed, but then you have no way to further slow or stop the vehicle until they cool down.
Your pretty much dead wrong and obviously have not used a vehicle with TOW/HAUL feature.
I HAVE towed BEFORE there ever was such a thing as TOW/HAUL, my first experience with TOW/HAUL was just amazing, all I had to do was just let off the gas pedal as I started descending a hill and the transmission downshifted and kept the whole rig from gaining speed the entire way down the hill.. Several hills were 6 miles long at 10%-11% grades! That truck was the 2006 F250, what a advancement in towing, before then, yeah, always manually poked the gearshift into the next lower gear..
Newer vehicles with advanced features HANDLE the upshift and downshift hill assent and descent gear changes WITH ZERO INTERVENTION AUTOMATICALLY.
This is far, far different from the days of old with a the manual "THREE ON THE TREE" or floor mounted "Handshaker".
OP HAS TOW/HAUL, they DO NOT NEED to "baby sit" every second of the gear selection. They can of course if they feel uncomfortable can OVER RIDE the gear selection that the TOW/HAUL selected just by TAPPING or TOUCHING the brake pedal lightly and the transmission will automatically downshift to the next available gear.
One of the nicest things I have found on TOW/HAUL on my Fords has been the fact that the shifts tend to be spot on the money and silky smooth.. I rarely have to tap the brakes to over ride or even ride the brakes..
Heck, I have a steep grade to get into the next town from me, 11% grade for 1 mile with not one but TWO stoplight intersections at the bottom.. My TOW/HAUL will and does downshift ALL THE WAY TO THE BOTTOM without me having to manually do a thing other than touch the brake pedal if needed. I only have to apply some brakes just before the stop lights and by that time the transmission is down to 2nd or 1st already.
Some folks just can't get that "trucker" manual mentality shift thing out of their head like you are stating..
And by the way, read the manuals, you NO LONGER have to take things out of "OVER DRIVE", that once again is an old school train of though that is not needed any longer.. Let the power train control figure out what gear to select and you will find that it does not "hunt" gears like older much more underpowered vehicles.
Newer transmissions also are designed to shift more since they have more gears to select, big difference in shifting between a 4 speed auto and a 10 speed auto.. If you don't like transmission that shifts a lot, don't buy a 10 speed as gears are very short between each..
Maybe GMs TOW/HAUL doesn't work as well as Ford but I can attest to the fact with my Fords, I am no longer trying to micromanage what gear I am in..
Perhaps you should try a Ford?