Towing Issue

sc4808 · March 30, 2009

I purchased a 2008 Silverado CC Last Summer with the 5.3L and 3:73 Gears.

When towing my travel trailer, the truck pulls it nicely except for one issue, when on the Interstate rolling along at 65-70 MPH and cruise set I run in 3rd (Not Overdrive) and on the slightest grade, the transmission will downshift to 2nd gear which is horrible at 70MPH. Now if I disengage cruise just before the hill and handle the throttle myself the truck pulls nicely and only looses a couple of MPH without downshifting.

Now of course I realize that the cruise is just trying to maintain the speed and when that speed starts dropping, the truck downshifts in order to try and maintain the speed, it just seems overly aggressive in the downshift profile, I mean when I am running at 70MPH in 3rd, I am turning around 3000 RPMs, and when I get this unnecessary downshift to 2nd, it will jump to 4500RPMs.

Can this downshift threshhold be changed with a programmer, I know that the upshift points can be changed but not sure if the downshift points can be modified.

I hate to think that I have a new truck that I cannot use CC on when on long trips.

VR021302 · March 30, 2009

How much are you towing?

66nova · March 30, 2009

I purchased a 2008 Silverado CC Last Summer with the 5.3L and 3:73 Gears.

When towing my travel trailer, the truck pulls it nicely except for one issue, when on the Interstate rolling along at 65-70 MPH and cruise set I run in 3rd (Not Overdrive) and on the slightest grade, the transmission will downshift to 2nd gear which is horrible at 70MPH. Now if I disengage cruise just before the hill and handle the throttle myself the truck pulls nicely and only looses a couple of MPH without downshifting.

Now of course I realize that the cruise is just trying to maintain the speed and when that speed starts dropping, the truck downshifts in order to try and maintain the speed, it just seems overly aggressive in the downshift profile, I mean when I am running at 70MPH in 3rd, I am turning around 3000 RPMs, and when I get this unnecessary downshift to 2nd, it will jump to 4500RPMs.

Can this downshift threshhold be changed with a programmer, I know that the upshift points can be changed but not sure if the downshift points can be modified.

I hate to think that I have a new truck that I cannot use CC on when on long trips.

Are you running in Tow/Haul mode?

How much does your trailer weigh?

A custom tune can change out shift/down shift points and give a little more power so maybe a down shift is not needed. I would also try towing a few mph one way or the other to see if it keeps your motor in the "sweet spot" where it does not need to down shift.

redvett · March 30, 2009

Are you using the tow/haul mode?

svensk · March 30, 2009

Are you using the tow/haul mode?

+1

If you're on the interstate you should honestly be able to be in OD with tow/haul, and cruise on (especially at 70mph). When there is a grade change it will just downshift to 3rd.

sc4808 · March 30, 2009

Yes I am using the Tow/Haul mode, I wish it would pull it in Overdrive but it won't, when in OD even on flat ground it keeps shifting in and out of OD.

My trailer Gross weight is right at my tow rating 7500Lbs, but It usually runs around 7000Lbs.

My 03 seems to handle the trailer a little better than the 08, I have pulled it all over the country with the 03.

wages999 · March 30, 2009

My 2004 does the same thing in tow/haul when I tow a car trailer behind it. If I tow in overdrive, it is really quick to downshift to third and then immediately to second. Usually I'm running around 2,000 rpm's in overdrive, then jumps to about 3,200 in third and the pegs up to 5,500 rpms in second. I think GM did a bad job of programming the downshifts in tow/haul mode. I've gotten use to kicking off the cruise control when I approach a hill.

VR021302 · March 30, 2009

I purchased a 2008 Silverado CC Last Summer with the 5.3L and 3:73 Gears.

When towing my travel trailer, the truck pulls it nicely except for one issue, when on the Interstate rolling along at 65-70 MPH and cruise set I run in 3rd (Not Overdrive) and on the slightest grade, the transmission will downshift to 2nd gear which is horrible at 70MPH. Now if I disengage cruise just before the hill and handle the throttle myself the truck pulls nicely and only looses a couple of MPH without downshifting.

Now of course I realize that the cruise is just trying to maintain the speed and when that speed starts dropping, the truck downshifts in order to try and maintain the speed, it just seems overly aggressive in the downshift profile, I mean when I am running at 70MPH in 3rd, I am turning around 3000 RPMs, and when I get this unnecessary downshift to 2nd, it will jump to 4500RPMs.

Can this downshift threshhold be changed with a programmer, I know that the upshift points can be changed but not sure if the downshift points can be modified.

I hate to think that I have a new truck that I cannot use CC on when on long trips.

Are you running in Tow/Haul mode?

How much does your trailer weigh?

A custom tune can change out shift/down shift points and give a little more power so maybe a down shift is not needed. I would also try towing a few mph one way or the other to see if it keeps your motor in the "sweet spot" where it does not need to down shift.

Any suggestions of who to use? Kool-Aid perhaps.

Also, since you mentioned ur towing around max weight, try dropping to 65MPH, and dont use cruise on hills, cause the system has no clue how much u r towing, and will give as much throttle as required to maintain speed.

sc4808 · March 30, 2009

Will an over the counter (Hypertec) programmer make the changes I need on the downshift threshhold.

VMax2007 · March 30, 2009

Edit...Nevermind, I thought you were in Texas.

VR021302 · March 30, 2009

I might be wrong, but I dont think it will on the GMT-900

C & A s Dad · March 30, 2009

Mark, A couple of things I would suggest. You are towing 7,000 lbs and it is a Camper. Also spelled "brick". I tow a 29' 6500lb camper as well with my '02 Yuk XL. Less HP than you have but I have 4.10 gears. Towing a boat or a car on a trailer is an entirely different set up so when talking to others about trailers and weights, ask what they are towing before you begin taking their advise.

I would have to agree with what Tex Mex said about the cruise. The system is simply trying to maintain speed and dropping a gear is what it is going to do. It cannot anticipate a hill or "soft pedal" it to keep from dropping a gear.

I tow in 3rd with T/H engaged. At 55 the 4.10s have me in the 2400 RPM range and I can easily maintain speed on moderate hills without straining the 5.3 in any way. However, I have never run the cruise when towing. If I chose to drive close to 70, I could run in OD because my Revs are still in the 5.3s sweet spot and it will do fine there. I can use OD at slower speeds but the slightest hill puts it back in 3rd and gets the revs back in the 2200 to 2400 range. Right where my 5.3 likes to run.

Now, here is the statement that gets some people excited. It is simply my opinion and what I do. If you do not agree, that is fine. I feel very strongly that 70 MPH towing a 7,000 lb brick with a 1/2 ton truck to too fast. This is even fast for a 3/4 or 1 ton, but certainly above what I would consider safe limits for a 1/2 ton truck. I am typically towing on 2 lane roads so 50 is my norm, 55 would be tops. When I tow on an Interstate, I will increase it to 60 but that is about it. I have never had any issues, I have a good brake controller, a good WD hitch, good tires etc. I just feel more comfortable at these speeds with my family in the truck and for those on the road around me.

Again, not "gettin in your biz" with the speed thing. This is just what I have decided to do.

66nova · March 30, 2009

Will an over the counter (Hypertec) programmer make the changes I need on the downshift threshhold.

IF you want to go with a handheld, don't waste you money on a hypertec atleast buy a Diablo. I'm not sure if it can adjust the downshift points, but it is the most adjustable (as close to a custom tune) handheld available.

I personally would still look into a custom tune and/or some 4.10 gears.

And +1 on slowing down to 65 or less when towing close to your weight limit. Especially if you are towing around the Oklahoma/Texas area.

VMax2007 · March 30, 2009

Will an over the counter (Hypertec) programmer make the changes I need on the downshift threshhold.

IF you want to go with a handheld, don't waste you money on a hypertec atleast buy a Diablo. I'm not sure if it can adjust the downshift points, but it is the most adjustable (as close to a custom tune) handheld available.

I personally would still look into a custom tune and/or some 4.10 gears.

And +1 on slowing down to 65 or less when towing close to your weight limit. Especially if you are towing around the Oklahoma/Texas area.

The Diablo does not support any TCM changes yet, so, NO it will not adjust the downshift parameters.

Go custom! Kool-Aid is nummy.

sc4808 · March 30, 2009

Thanks for all of the advice, sounds like I should have bought a bigger truck after all.

I have been towing for years and I have used many trucks, from 1 tons down to 1/2 tons and in my opinion it has always been better for me to tow my size travel trailer with a 1/2 ton truck. I only tow aprox less than 2% of the miles that I drive so instead of sacrificing ride quality (heavy duty truck) during the 98% of time that I am driving the truck I would rather sacrifice a little towing ability since I tow such a small percentage of the time.

Don't mistake that as sacrificing safety, I don't skimp on that, I use the proper equipment and drive safely, and as far as the speed thing, the issue I have is worse when towing slower, say 55 or 60 because the engine is just above idle and not in its power band.

Now as far as stability is concerned, which is where a few people seemed to be going, that has not been an issue, the truck and trailer are rock solid when towing, no sway or ill handling, even at 70 MPH, ROCK SOLID, that much I have always been impressed with on GM products, my 03 was just as good.

I just feel that the downshift pattern is just a bit aggressive on these new trucks and was wondering if there was a way to modify it.