When to downshift

[NCMODELA]

Hi, I tow a approx. 6000lb trailer with a 03 Yukon xl 5.3, 3.73 gear. I took it for a drive today (middle NC) and it was in third, hit a small to medium hill (bump in the road to western people) at 2800rpm doing about 65 to 70 and it started slowing down, hit the gas some rpm went to 3000 and kept speed around 62 or so. hit the gas harder just to see what would happen and how it would react, it downshifted into 2nd, 4500 rpm and it pulled and gained speed up the rest of the hill. I was just wondering from people who have towed with similar vehicles do you let it downshift or let it lose a little speed then gain it again after the hill? It seemed really excessive to downshift into 2nd for that hill because I would have maintained 60-62 going up the hill.

When do people decide to floor it to downshift excepet on mountain grades? do you have to slow down a lot before you do it?

[Gale_Hawkins]

Fixed Sight Training wrote:
In my '03 5.3 Tahoe I rarely floor. I keep the throttle steady and at 50ish I downshift to second and keep it about 3800 rpms. This is in the Rocky mountians and it seems to be very happy pulling at the high 3k rpm to 4k. I also hold it in second until I can let way off the gas and let it shift easily into third. My TH is about 6500 normally loaded and my GCVW is in the 12,500# range. I usually get just under 10 mpgs pulling in the mountains.

It seems like at 3400 rpms and less it starts to really struggle. It's always better for the engine to pull under load at higher rpms.

I think 3500 RPM is MIN any gas engine should be run at loaded in the hills. We have not towed more than a two horse steel trailer loaded with hay with our 5.3 but have put 18K miles on the MH 454 TBI engine and four speed transmission with a few thousand in the Rockies a couple years ago.

The wide open throttle up shift point is 4000 RPM. While the red line is more like 4500 I do not like to grind at over 4000 RPM which in 50 MPH in second gear I remember from pulling Grapevine going south in CA.

Any vehicle out of OD and in the hills towing loaded 60 MPH would be MAX RPM. Engines and transmissions are like men. Run them maxed out they do not last as long. 🙂

While it is fine to run a GM transmission without the torque converter locked up (lock up feature was not an option until in the early 90's) it is not fine to climb below 3500 due to heat damage to the transmission and engine.

Going up to Mt Rushmore I was able to drag out some of those hills at 2800 RPM in 3rd but temps would start to climb but when going to 3800 in 2nd it ran cooler than at 70 MPH in OD in mid KS.

Manually downshifting (by going to the floor) then moving the shift lever to lock it into the lower gear works best for me where going up going up or down a big hill. If you have a newer 6 speed GM transmission the computer will do this for you when you down shift manually I noticed on a rental.

If one gives it more gas and there is not gain in speed/RPM and you are not in 1st gear then you are one gear too high.

Now with some V-8 and most all V-10's 4500 RPM may be the best RPM when loaded in the hills.

Again by taking off and leaving foot on the floor note the RPM of the automatic shift up point. This is your safe RPM when climbing or descending (engine braking).

Note we are only discussing GAS engines. Do not consider your MPH numbers when towing a load in the hills. It is only a by product of being in the correct gear and RPM range.

Higher the RPM is near the WOT shift point the less gas used and wear and tear on the engine and transmission I find.

Climb a mountain in a gear that more gas does not give more speed can cook a transmission over time.

[Peg_Leg]

Search online and find the power curve for your engine. Once the RPM's drop out of the power band, downshift and bring the RPM's back into range. You won't be flooring it and you won't be the first one up the hill but your drivetrain will be happier in it's old age.

[Terryallan]

Let it top the hill at 62. No need to run 70, especially since your TT tires are only rated for 65 mph. So in truth, at 70 mph you are out running your tires.

[ktosv]

That shift from 2800RPM to 3000RPM is the torque converter unlocking in 3rd gear. Run the transmission to long with the torque converter slipping and you will heat the transmission fluid. Get it hot enough and that is bad.

Any tow vehicle that I had that couldn't pull hills with the torque converter locked I had a tranny temp gauge added so I would know if and when I had to shift it to the next lower gear or slow down for it to lock back up.

It all depends on how long the grade is and how steep it is if you force it to second.

[Fixed_Sight_Tra]

In my '03 5.3 Tahoe I rarely floor. I keep the throttle steady and at 50ish I downshift to second and keep it about 3800 rpms. This is in the Rocky mountians and it seems to be very happy pulling at the high 3k rpm to 4k. I also hold it in second until I can let way off the gas and let it shift easily into third. My TH is about 6500 normally loaded and my GCVW is in the 12,500# range. I usually get just under 10 mpgs pulling in the mountains.

It seems like at 3400 rpms and less it starts to really struggle. It's always better for the engine to pull under load at higher rpms.

[Vulcaneer]

It all depends on how close I am to the top of the hill. If I am losing too much speed to carry the hill, I downshift. Especially if less than 3/4 of the way to the top. And lost more than 10% of the speed. Otherwise, I might ride it out. Depending on my mood, the traffic, highway, or secondary road.

[wilber1]

I don't care for the flooring method either, I shift down when I think it is necessary. Experiment and figure out what works for you.

[coolbreeze01]

I downshift as needed. Don't care for the flooring method. Have fun.