Towing in 3rd gear

I have a 2004 Silverado Z71, 4.8 Auto, 3.73 rear end with towing package. I tow a boat that with the tandem trailer weighs about 4000#. Now I have have always thought that you should not use over drive
while towing, but use 3rd gear. I thought I saw something in a gm brochure that indicated towing in OD was OK provided you used the tow/haul mode. I am somewhat dubious about that. My previous truck was a 99 1500, 4.8 and had no problems pulling the load using 3rd gear. What do you guys think?
hank
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I'd kinda be interested in what others think about this also.. I have no idea if it's just my truck but when using the tow/haul mode in OD my transmission shift very hard.. I have no idea if this is normal or not but I kinda doubt it. I like the idea of tow/haul mode because I see where it does raise the shift points and all of that.. But like I said my '99 4x4, 5.3, 3.73. slam shifs at 2500rpm.. and since I dont' like that I just use 3rd. info?
Adair
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Hank,
The following is copied (edited short form) directly from the Silverado Owners Manual:
If you have an automatic transmission, you can tow in DRIVE (D). You may want to shift to THIRD (3) or if necessary, a lower gear selection if the transmission shifts too often. (e.g., under heavy loads and/or hilly conditions).
Tow/Haul Mode (If Equipped)
Tow/Haul is a feature on A/T equipped vehicles that assists when pulling a heavy trailer or hauling a large heavy load.
It's purpose is to:
1. Reduce the frequency and improve the predictability of transmission shifts when pulling a heavy trailer or hauling a large heavy load. 2.Provide the same solid shift feel when pulling a heavy trailer or hauling a large heavy load as when the vehicle isn't pulling or carrying a load. 3.Improve control of vehicle speed while requiring less throttle pedal activity when pulling a heavy trailer or hauling a large heavy load.
The Tow/Haul Mode feature is most effective when the combined weight of the truck and trailer is at least 75% of the truck's Gross Combined Weight Rating (GCWR). It is most useful under the following conditions:
1.When pulling a heavy trailer or hauling a large heavy load through rolling terrain. 2.When pulling a heavy trailer or hauling a large heavy load in stop and go traffic. 3.When pulling a heavy trailer or hauling a large heavy load in busy parking lots where improved low speed control of the vehicle is desired.
Operating the vehicle in Tow/Haul Mode with no trailer or load won't cause any damage but will result in unpleasant driving, engine, and transmission characteristics and reduce fuel economy.
end!
Judging from the specs you gave I think your truck has a trailer hauling capacity of (maximum trailer weight) 7300lbs +-200lbs. I don't know your GVW but if you add that to the 4000lb trailer weight that should be your Gross Combined Weight. Now add the Gross Vehicle Weight and the Trailer hauling capacity to get the GCWR, divide by 75% and that should tell you whether you should be using the Tow/Haul Mode or not.
I'm sooooooooooo.....confused!!!!!!!!!! (:
As to hauling in 3d all the time I don't think it's a good idea. It ruins gas mileage and could cause overheating.
Jimb

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Rebel48 wrote:

Well, you raised the exact question better than I would have done. I have listened to many individuals on this NG such as Gary, Doc, Shade and even Marsh and all his alter egos.I think that using the tow/haul mode increases pressure in the transmission to ensure that things don't slip? Does keeping it in OD raise the temp as opposed to running in 3rd? I'm not confused just ignorant on this issue. I value most everyone's opinion on this issue, particularly the the trans experts.
hank
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Having been a GMC sales manager when the new generation trucks were introduced, 99-00, I went thru all the GM training concerning towing and the 'tow haul'. In addition, I have regularly towed a car on an open trailer (approx. 5000 lbs) with both a 00 GMC Sierra Ext Cab with the 5.3 and a 01 GMC Yukon Denali with the 6.0.
According to GM, as long as you are within the tow limits of the vehicle, its is OK to tow in (D) or overdrive instead of downshifting as was recommended in the earlier models. This is, of course, if you are using the tow haul mode. The tow haul mode firms up the shifts and extends the shift points. Also, if you are in hilly or mountainous terrain you will need to downshift as always.
In my personal experience I have always towed in Overdrive with the Sierra and Denali, using the tow haul. I tow in mostly level or only slightly hilly terrain, and if I happen to go into the mountains, I will downshift. I have had absolutely no problems, and the tow haul mode does exactly what it is supposed to do. It keeps the engine right in the pulling range, not letting the rpm drop to low. GM put a lot of effort into this, and it seems to be worth it.
Jerry H--retired GMC sales manager

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As you were a sales manager, you no doubt had "new" vehicles at your disposal and therefore no 'problems' but... that raises this question: What are the 'long term' ramafications of towing in OD vs third and OD tow/haul for trans longevity? What kind of trans life can we realistically expect to see as result? When can we expect trans problems as a result of towing? Respectfully Rolf
----- Original Message -----
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Also realize that the factory is now designing cars to be replaced every 100,000 miles.
Thank you, no.

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hank wrote:

I've towed 6000lbs+ behind my old 5.3 Avalanche in OD, a good amount.
I like to use Tow/Haul with that kind of weight, for the more solid feeling shifts, and better shift points.
The only time I'd drop it into 3rd, was when I was on the highway, and driving around 60mph -- the upshift / downshift point for OD and converter lockup. I didn't like dropping below 60, having the tranny kick down and the rpm's going up to 2800 or so, and then kicking back up a gear once above 60.
I *really* don't think there is any worry in towing in OD anymore with these lockup converters. Once your in OD (undeer Tow/Haul), you're locked in gear, nice and solid. No slipping.
-marc
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