Brand new to this forum. Questions about re-gearing my 26’ HD

[BDS my HD]

Hello hello looking forward to expanding my knowledge of the 2026 2500 HD that I just bought.

 

Truck has 3500 miles on it four-wheel-drive crew cab and I’m about to put a 6 1/2 inch BDS lift on it 18 x 10 -25 offset with 37’s

 

Already have the wheels and tires just waiting on the lift install in about three weeks

 

Question what surprises am I not gonna be happy with?  I’m not new to lifted trucks so I know that acceleration towing gas mileage all that is affected..

 

Question is those of you that have this truck this powertrain with a 10 speed Allison and have done the mods that I’m doing,,, how bad is it? Is that Allison constantly gonna be hunting for the right gear to go into? And what about towing, acceleration, fuel consumption as mentioned? 

 

Lastly how come I can’t find any ring pinion gear set up for these axles and when could I expect to see them?

 

I apologize if there’s any typos I’m doing speech to text on my iPhone.

 

 

[davester]

Note, this can void your whole warranty, if you don't get the speedo/odometer calibrated for it, as your mileage will be off.

[No F-bdy Bs]

Diesel or gas? 

The 37s will obviously, drastically reduce mpg, but the gasser will take a bigger hit to mpg, and power. 

Rough guess, but I'd estimate at least a  2mpg hit on the diesel, and up to 4on the gasser. Maybe more. 

 

I wouldn't sweat a gear change on a duramax at all, and unlikely on the gasser either. You're obviously not concerned with acceleration or towing, and the 10spd will find itself in the right gear without much hunting, if any. 

 

If towing, mpg and acceleration are a concern, you're doing the wrong mods. 

Either leave it alone, or do the lift/tires and let the chips fall where they may. 

Edited June 16 by No F-bdy Bs

[BDS my HD]

Towing power and I guess MPG matter that’s why I may end up going with a gear swap as soon as they’re available for this truck if I’m correct

[Another JR]

Why the extreme lift?  

[chris21]

37's are within 10% of stock. The 10 speed has a really low 1st gear. Neither engine will really struggle.

 

There is only one device currently that can trick the computer to correct for tire size, there are no programmers that work on the global B trucks that I am aware of, so programming the transmission shift points for re-gearing isn't possible at this time that is why there are no parts available for it.

[No F-bdy Bs]

Any 37 lin tire + wheels is adding a considerable ammt of unsprung weight, regardless of the height difference, so I stick to my mpg estimate. 

Also, front and rear gear swaps are probably pushing $3k after labor. 

 

[chris21]

3 hours ago, No F-bdy Bs said:

Any 37 lin tire + wheels is adding a considerable ammt of unsprung weight, regardless of the height difference, so I stick to my mpg estimate. 

Also, front and rear gear swaps are probably pushing $3k after labor. 

 

I didn't mean to seem dismissive of hurting mpg. Lifting the truck while still using stock tires would hurt mpg too, I was just saying that both engines have plenty of low end combined with a low first gear that drivability would be fine with stock gears.

 

Towing with a significant lift sucks regardless of engine, transmission and gear ratios. And suspensions that allow extra travel don't carry extra weight well. If you're using the truck to tow or haul near capacity a big lift isn't great and reduces the the truck's capacity and these trucks are too heavy and long to be good for serious off road.

[BDS my HD]

I guess I don’t look at it as extreme I had 11 inches on a 1500 ram with 38 I had a 4 inch on a OBSF350 with 37 I had a 4 inch on an OBSF 250 with 35 and I’m not really into off-road I just appreciate good-looking vehicles this truck will never be offloaded other than maybe a dirt road 
 

I mean the factory is even putting 37 on Broncos etc. Raptors they know what people want

[BDS my HD]

I don’t do offloading other than a dirt road literally for me it’s more about the look which I really appreciate a nice looking truck and I like sitting a higher and not just because I’m 5 foot seven lol..  I’m also not compensating for anything lol..  but I truly think it’s safer on the road the higher you sit you have better visibility generally speaking especially a few of your Sideview mirrors adjusted correctly. They do make a programmer rough country does they’re $1000 for these new 2500s but when I do a gear swap that would be a moot point. A lot of the shops that I go to in my area they’re all saying the same thing that Yukon Detroit axle Eaton Spicer Richmond they don’t have gear shot for these trucks which surprises me because hasn’t this body style been out since 2020? I’m hoping soon they have something because yeah I’ll have to spend the 3K to get both axles done. Thank you for all of your response responses. I apologize if there’s any grammatical error errors as I’m doing speech to text on my iPhone without proofreading 

[chris21]

37's would probably fit with a 3" lift. GM only has two gear ratios for these trucks 3.73 for gas and 3.42 for diesel. And they can't be programmed for anything else at the moment. The rough country module just corrects the speedometer and odometer to adjust for tire size it's not a programming device.

 

You haven't said if your truck is gas or diesel, but for a gas truck the 10L1000 with 3.73 gears has a lower final drive ratio than the 6L90 it replaced would if it were swapped to 4.10s. GM used the same 3.73 gearing in 6 speed gas trucks. I don't think you'll have any issue running 37's with the 10 speed other than the reduction in mpg and towing/weight capacity which is as much of a function of the lift as the tire size.

[newdude]

3 hours ago, BDS my HD said:

but I truly think it’s safer on the road the higher you sit you have better visibility generally speaking 

 

 

That is a huge misconception.  

 

Bigger does not always equal safer.  Modifying does not make it safer either, with exceptions.

 

Think of this.  Your truck in stock form is capable of emergency maneuvers, proper stopping distances, its handling is designed around the factory wheel/tire packages, etc.

 

37s and a lift?  Now you've affected your braking distances, handling and ride control.  You've raised your center of gravity higher.  Your front visibility is now obstructed more than stock, same for your rear.  Does it look cooler?  Yes.  Does it now work as good as it did from factory on road?  NO.  

 

 

As for my mention of exceptions?  Say you had a sedan or crossover.  They typically come with all season tires.  If you swap out for a performance all season or a summer tire, you improve your car by lowering its stopping distance (better braking because of traction) and improve the handling (regular and emergency) of the vehicle.  That is an actually improving modification.  My old 2019 LD 1500, I ran UHP all season tires on 20in wheels in a factory offered size.  It improved all aspects of how it drove over the Duratracs it came with from the factory in the stock 18" tire.  

[BDS my HD]

Chris 21 I appreciate your constructive response. !!  

 

The 6.6 is gas.  Correct me if I’m wrong but by recalibrating the speedo you’re correcting the shift points of the transmission on these trucks.?.

[chris21]

50 minutes ago, BDS my HD said:

Chris 21 I appreciate your constructive response. !!  

 

The 6.6 is gas.  Correct me if I’m wrong but by recalibrating the speedo you’re correcting the shift points of the transmission on these trucks.?.

I'm pretty sure it doesn't actually recalibrate the speedometer it just changes the wheel speed sensor inputs to the computer. The truck still thinks it has stock tires.