GM 6.0 gear searching.....

I had a 2009 GMC 2500 with a 6.0 in it. I used manual shift and kept it in 5th gear and ran at highway speeds of 65 consistently without any issues. You are doing more harm by running it in automatic mode pulling that heavy of a load.

One question I did not see asked:

Stock tires? If you're running oversize tires they have the effect of soaking up power and effectively raising your axle ratio (lower numerically).

BurbMan wrote:




Intheburbs, the caption on your pic should be "Last pic I took before the trans blew."

Well, the first time I had the trans approaching 240° was our trip to the Grand Canyon/Utah/Colorado, and that was 4 years and 50,000 miles ago. Still the original transmission, still shifts perfectly.

My motto is, "Know your equipment." A close friend of mine is a transmission validation engineer at GM. He spends most of his time at the Milford proving grounds, has his license for driving there, and gets to do some pretty cool stuff with some great cars and trucks. His first job/project at GM was validating the 6L80/6L90 transmissions. I asked him about my plans and the temperatures I was seeing, and he assured me they did much worse in validation.

Granted, my experience is a data point of exactly one, but most of the components on the 2500 Burb, as you probably already know, are total overkill for the application.

And, unlike your '01 that uses Dex 3, the Dex 6 in the GMT900 trucks is a substantial improvement and can take some serious heat. The "trans hot, idle engine" warning only comes on at 265°. I also change out the fluid religiously.

ericpatt wrote:
Thanks everyone! The trip went well. Madison, WI - Bowling Green, KY. Tow/haul shifted to manual and limited trans to 5th gear. Highest trans temps got was about 165-170. On several flat stretches I was able to get it to hold 73-4mph in 5th gear around 2500rpm. Was happy with that.

Otherwise, it was holding 3-3300rpm to keep 65-70 through rolling hills..

That is right where that engine lives quite happily and makes it's best power. I spent 10 years towing with a Chevy 2500HD 6.0L with 4.10 gears and the 4L80E transmission. It towed my TT pretty well but always downshifted on hills.

I found in eastern Kentucky that it didn't go much of anywhere under 3,000 RPM. However, once you hit the magic number of 3200RPM...up up and away!! :E I looked up torque curves a long time ago and seem to recall that 3200 - 4200 is the real meat of the of the curve on this engine. You'll pull up a hill just fine if you keep the engine in this range.

KJ

Hi Eric, glad the trip went well! I agree with most here, don't waste time on intake/exhaust, if you want more power then do an axle gear change from 3.73 to 4.10 (no 4.30 on GM, next stop would be 4.56 and that's too tall for what you're doing). Both axles will cost around $1500 to do at a good axle shop.

Aside from that, it sounds like you stopped the hunting by limiting the trans to 5th gear. One of the ways that the mfrs maximize fuel economy is to program the ECM to upshift at every opportunity, and it can be frustrating on rolling hills. The wind is also a factor when towing a big hard-sided trailer. As soon as the load on the motor abates a little, the trans will try to upshift if you let it, but if you need power again in 5 seconds, it will downshift to deliver.

FYI, your trans temps are right where they should be, I have never seen higher than 205 even going up a steep incline. The factory cooler on the HD trucks has been moire than sufficient in my experience, it's mainly the 1500 series trucks that benefit from more trans cooling.

Intheburbs, the caption on your pic should be "Last pic I took before the trans blew."

ericpatt wrote:
Thanks everyone! The trip went well. Madison, WI - Bowling Green, KY. Tow/haul shifted to manual and limited trans to 5th gear. Highest trans temps got was about 165-170. On several flat stretches I was able to get it to hold 73-4mph in 5th gear around 2500rpm. Was happy with that.

Otherwise, it was holding 3-3300rpm to keep 65-70 through rolling hills..

4.10`s or if 4.30`s are available will allow you to use 5th gear. and will gain you .5 mpg because the engine will no be working as hard!

I went from 3.73 to 4.30 and it was the best thing I did. I could never use O/D. I can now cruise in O/D at 70 at 2700rpm as opposed to 3200 in 3rd at 67! (it used to hunt for O/D at 65-67) granted I have a 4 speed, but the idea is the same!

PAThwacker wrote:

lawrosa wrote:

goducks10 wrote:
Change your rear end gears.

Dude he has a 6.0 and 3;73's... Its bad enough he gets 2 mpg...

Dont change rear gears... Just ride in 4th gear with that load as I stated above in my post...Use tow haul mode!!! Its that little button on the shifter handle..

I guess no one read my post and just reply for the heck of it..

2500 burbs with 6.0 all had 3;73 AFAIK.. and can tow 9000 plus...

What 2500 6.0 3.73 tows 9000lb?
My 04 is rated to 7600lbs. 07 on up can’t handle tongue weights of 7600lb trailers.

He has a 2012.....

Chevy Suburban, GMC Yukon XL 2500
2500 Long Wheelbase 2WD 6.0L V-8 9,600
2500 Long Wheelbase 4WD 6.0L V-8 9,400


https://dcd96xmek71bc.cloudfront.net/trailerlife.com/2012_towing_guide_lo_res.pdf

lawrosa wrote:

goducks10 wrote:
Change your rear end gears.

Dude he has a 6.0 and 3;73's... Its bad enough he gets 2 mpg...

Dont change rear gears... Just ride in 4th gear with that load as I stated above in my post...Use tow haul mode!!! Its that little button on the shifter handle..

I guess no one read my post and just reply for the heck of it..

2500 burbs with 6.0 all had 3;73 AFAIK.. and can tow 9000 plus...

What 2500 6.0 3.73 tows 9000lb?
My 04 is rated to 7600lbs. 07 on up can’t handle tongue weights of 7600lb trailers.

Iraqvet05 wrote:
Cold are intakes in my experience are a waste of money.

Ditto.... and why they are called "Cold Air Intakes" is a mystery, because most of them don't draw in cold air from outside the engine bay. Most of them consist of a big cone shaped filter with a metal shield around it, with no sourcing of air from outside the engine bay.

On my 09 Duramax (same body style as the OP's SUB), the factory intake draws in air from outside the engine bay, which is the case with many other GM trucks as well.

goducks10 wrote:
All GM 2500 trucks now come with 4.10 standard. Must be a reason.

I had a 2011 2500 HD CC with the 6.0 and 3:73. I traded it in on a 2015 3500 CC with 4.10 and it was much better. With a size larger tires than OEM I got 13-14 mpg not towing and down to 5-6 at 30K combined. If you are really working the suburban your actual towing mileage my go from not changing to perhaps improving slightly with the 4:10's. I think it is the best bang for the buck improvement you can make for what you use the SUV for. You might see a 1 mpg reduction in hwy nontowing mpg. The 4:10's are a much better match for the 6.0 than is the 3:73 if you towing with it. Love that motor.