Re-Gearing my rear end???

[Concept1]

I have a 2006 Duramax thats lifted 8 with 37 in tires. I know I get terrible mileage, you have any suggestions if its worth doing? I know its going to be around $1100.00 or so to do. i can almost watch my gas guage falling doing 70 or so while towing...

[sigepmock]

Two things hurting you......loss of mechanical advantage from the taller tires and at freeway speed a ton more air resistance. I run 35's on my Dmax and don't notice the power loss too bad but I do noticed the added wind resistance...especially on a windy day like today.
Your truck has 3.73's and you gou go to 4.10's or 4.56's. I ran 4.56's on my 03 2500 with the gas motor and 35 inch tires and it really helped out. What RPM's are you running at 70 mph?
Chris
$1500 to do front and rear. $750 or so for a 2x....

[djunkie]

Keep in mind that if it is a 4x4 you will have to do the front diff also. Unless you plan on NEVER using 4 wheel drive.

[cc322]

With 35's 4.30 would be good, since you are running 37, 4.56 may be you answer. Here is a link you can check out, or give them a call, very cool guiys and are first class in there work. djunkie is correct you need to do front and rear if its 4x4, if 1,100.00 is for both including bearings thats a good deal.
http://www.gounitrax.com/default.htm

[Beer-30]

Your torque will come back up, but it's not going to change your mileage. You still have the rotating mass of those tires/wheels that require more hp/tq to turn them than smaller. Like mentioned before, you have exposed alot more of your vehicle to headwinds and just plain wind resistance alone. Cranking the gears back up is going to bring your rpm back up and probably hurt mileage even more.
Nothing is free.

[Concept1]

Hmmm I think it was 1100,00 for just hte back, its a 2WD. If I go up in the gears wont that mean the rear end will be helping the towing out alot? It seems to me the the turbo is making up for the size of the tires and the weight, going to the 4.56 should take the pressure off the turbo so gas mileage should go back up right? I know its alot taller now and wind will play a factor but getting 6 MPG seems a little low to me.

[Concept1]

Two things hurting you......loss of mechanical advantage from the taller tires and at freeway speed a ton more air resistance. I run 35's on my Dmax and don't notice the power loss too bad but I do noticed the added wind resistance...especially on a windy day like today.
Your truck has 3.73's and you gou go to 4.10's or 4.56's. I ran 4.56's on my 03 2500 with the gas motor and 35 inch tires and it really helped out. What RPM's are you running at 70 mph?
Chris
$1500 to do front and rear. $750 or so for a 2x....
Ill have to check this weekend I didnt even look at that. I just assumed it would need 4/56 or higher so thats what I asked the dealership about. Should I be checking without the boat at 70 or with?

[STV_Keith]

If you are considering doing any power upgrades, do them BEFORE you consider gearing changes. Power makes all the difference with the diesels. With some more power, you may not want to spend the money to do different gearing.
Also, for just a bit more money, you might consider an underdrive unit instead. That way, you can still have those tall gears for cruising the highway, then use the underdrive when you want to tow.

[Concept1]

If you are considering doing any power upgrades, do them BEFORE you consider gearing changes. Power makes all the difference with the diesels. With some more power, you may not want to spend the money to do different gearing.
Also, for just a bit more money, you might consider an underdrive unit instead. That way, you can still have those tall gears for cruising the highway, then use the underdrive when you want to tow.
The power thing is the proplem I turn my chip down to the tow setting because on the power setting its even worse. My last 02 Duramax towed my 35 ft weekend warrior at 75mph and I get around 13 MPG with 35's. I dont see how it could be that much of a difference on this new truck. I agree with Beer-30 though I know Ihave to pay to play im just kinda stunned at the numbers the truck is getting on something that weighs 5000lbs and my old trailer thats weighs 14000 lbs. Im going to gear it anyway because I think thats the problem its only 750 at the dealership so im going to do that for sure, Ill see what happens after that!

[Beer-30]

Ya know, a friends '03 (520 ft lb) Dmax was getting between 8 and 10 pulling a 21' Malibu tourny boat. 2500 cc, 4X, stock height. After about the 25-30,000 mile mark, it had increased to about 14-15, depending on speed. Diesels take longer to break-in than gas. All the rotating parts have to make their new home. Rings have to get the cylinder walls scuffed to make a happy home.
Empty, freeway, I personally witnessed them fill up with 21 gallons and 422 miles on the trip odo.

[Concept1]

Maybe its just too new then, Im doing a cold air intake tomorrw and taking the power program down to the tow setting and see what it does after that, just for shi**t and giggles im taking the air filter out right now and blow it out to see if it makes a differnet, I can tell you that it is TOTALLY filthy, im sure that didnt help at all either..

[sigepmock]

Maybe its just too new then, Im doing a cold air intake tomorrw and taking the power program down to the tow setting and see what it does after that, just for shi**t and giggles im taking the air filter out right now and blow it out to see if it makes a differnet, I can tell you that it is TOTALLY filthy, im sure that didnt help at all either..
6mpg seems low. I'm seeing around 15mpg towing light on the freeway. 12 at the worst towing the boat in the heat. I see 2000 RPM's at 75mph and the truck seems to like that rpm but I don't tow that fast and I've only got the 5 speed Alli trans. You have the six speed so going with 4.56's should do you right for 70 mph. Right now you're lugging the motor pretty good with those tall tires and I'm sure that's hurting you. I only hear the turbo spooling up when I'm climbing a hill when towing...most other times the boost is running around the 5 to 6 psi range just cruising.
Re-gearing a 2x should cost you about $750 to $800 at a good shop. I wouldn't trust the dealer to do it. Find a specialist in your area that can do it right. I'm sure there is somebody on here that could point you in the right direction.
Good luck,
Chris

[Concept1]

Funny that you should say that because I was trying the dealer to avoid any warranty issues but now that i think about it ill just go to a 4X shop and not tell the dealer its been done. I kinda thought that it was lugging a little bit but i knew the power was there to make it work. Gonna take it to the lake again Sunday and watch the RPM's and track the mileage. Monday im gonna drop it off and have the rear end done and recheck it, either way with the rear end done I should see similar power with the chip turned down thats what im told is killing my gas.

[sigepmock]

Funny that you should say that because I was trying the dealer to avoid any warranty issues but now that i think about it ill just go to a 4X shop and not tell the dealer its been done. I kinda thought that it was lugging a little bit but i knew the power was there to make it work. Gonna take it to the lake again Sunday and watch the RPM's and track the mileage. Monday im gonna drop it off and have the rear end done and recheck it, either way with the rear end done I should see similar power with the chip turned down thats what im told is killing my gas.
Re-gearing it will get your motor back in it's happy operating range...kinda like propping a boat :) j/k
Just make sure you go with a good reputable shop. Re-gearing is more of an art than anything and finding the right shop to do the work is the key to a long happy ggearing life. If it's done wrong it will take out a lot of really expensive parts when it goes. Also make sure to follow the "break-in" procedure once you get the new gears in. Something like drive for 20 min's the stop and let the gears cool-off...then drive another 20 and let it cool off, and don't tow anything for 500 or so miles.....anyway follow the instructions of the shop that does the work. Proper break in is just as important as proper installation.
Chris