FWIW - I did ask Nitro two years ago about making them. I don't know if Nitro actually has any in house manufacturing though. They might. Just don't know. But they were not interested in doing it. That was a conversation in person with some folks there.

I reached out to USA Gear as I know they actually manufacture gears, not just sell them. I'll also send an email to Samgong in Korea to see about minimum order and pricing for a custom run. This shouldn't be a particularly complex thing for either one to do if they're willing to do it. It's all done via CNC machines that can cut pretty much any gear they want. Part of it depends probably on whether they have ring gear and pinion gear forgings that are close enough to work well. I think if Samgong is making some 8" or 8.2 diffs they probably could use existing stock. A 3.73 pinion blank and a 4.56 ring gear blank forging could be used I think. But they're experts on their processes. I'll update if I hear anything back and what the response is.

For a one-off, it's probably easier just to swap a housing for a 9.5 land cruiser and find an OEM rear e-locker axle with 4.10 gears. Those are pretty easy and cheap to find. For a group buy - maybe it'd be cheap enough to make it worth it. I think wholesale price is typically around $100 for a ring and pinion set, but I'm guessing the minimum order is pretty big if you have to cover the cost of new forging dies or you have to pay a big up front design/tooling fee.

Keep us posted on what you go with. I put 4.10s in my old JKU with 35's. Made a huge difference as far as "power." I'm interested in how this turns out and what you decide.

I have also been for a low 4 ish diff set but have not had any luck.

I don't know that I'm keeping my 4Runner a lot longer. But it's still not totally decided yet. I tried 4.56 and took them back out because I didn't like how low my mpg was on the highway. So my logic is that I'll just switch to a GX with the extra overdrive gearing and maybe then go 4.56. For the 4Runner I felt 4.56 was too deep of a gear for a small tire size change and 4.10 would be a better fit. But of course there are no 4.10 gears available, and any other options end up more expensive than just swapping my stuff over to a GX and selling the 4Runner. Either way - 4.10 might also be a good option in the GX for mild lift/tires.

I will update if I get any response back from either of those two manufacturers. I'm not sure I will get any response though. USA Gear doesn't do any Toyota stuff now. And the Koreans may not be interested. I think they'd sell a lot more 4.10 sets than 4.88. If someone like ECGS or Nitto asked, I'm sure they'd probably take it more seriously than from me. We'll see what happens.

I called the folks at Nitro and spoke about wanting a 4.30 option and they said it's just not worth it cost wise for most people. Even with me being only on 255/75r17 (32 inch) tires he said that 4.56 are perfect for that setup or even stick 31.5 tires. Especially at altitude with a little extra weight or towing a small trailer. Basically I would be at 2050rpm at 60 mph from his experience driving them with stock-ish sized tires. At Colorado 75mph speeds I would be right at 2500-2600rpm which puts me in a good powerband spot for 5th gear and would save me from downshifting all the time for tiny hills or headwinds. It would also probably keep the same mileage and not really impact me in his experience unless I add quite a bit more weight or go to 33s. From the sounds of it these things shouldn't have even left the factory with 3.73 gears.

I hear you on struggling to keep the 4runner. I love them so much, but for 2020 we need at least a reflash of the transmission shift points or something like 4.10 option from the factory. Driving this thing in the mountains unless you want to keep it floored the entire time makes me feel like those semis that get in the car right lane and turn on their flashers. I've been looking really hard lately at the ecodiesel JKU or now the new Bronco. Although both awesome vehicles, I love the bullet proof nature of the 4R and that's what's always drawn me to them. I really hope the 4R 6th gen blows the world's socks off because with the war about to take place between Ford and Jeep it could easily get left way behind!

IMO - nitro is wrong on that opinion. 4.10 is a big difference from 3.73. It's more different from 3.73 than 4.88 is from 4.56. If you were going to drop a ratio - 4.88 would be the one to drop and just to a 4.56 and 5.29 set.

Appreciate the input. I wonder why everyone is so opposed to offering 4.10's? In my original research it did seem like it would be darn near perfect for stock or 32 inch tires.

FWIW, I'm in on a group buy if someone is willing to make a 4.10 set for the 5th gen as long as it doesn't exceed $1,600 ish.

Assuming this is commonly known - but Toyota does make 3.91 ratio. To Toyota at least 3.91 is enough different from 3.73 to justify. I'm a little more skeptical of that decision. And I don't see much value for us in swapping to the 3.91 ratio. I'm still not totally sure why Toyota chose to make that extra ratio.

Toyota at one time made both 4.10 (41 tooth ring gear and 10 tooth pinion) and 4.11 (37 tooth ring gear and 9 tooth pinion) ratio 8" differentials. Why you'd ever do that is beyond me to even take a guess at.

As far as cost - I really have no reference to even guess what a small batch order would be. A typical gear retails for about $200-250, but I wouldn't hold my breath on it unless Toyota decides to put it in a model. The cost is mostly in the labor to install. And in our case - it's mostly just the huge PTIA it is to swap the carrier. Setting up a rear diff only takes around an hour or so. A front is more of a PITA, but maybe 2 hours. The removal and install takes me about 5 hours in the back and probably 5 hours in the front on my garage floor without a vehicle lift.

The FJ40 had 4.10 gears up until 1979 when they went to 3.73 claiming it would improve MPG. It didn’t as friends who had ‘79-83 40’s claimed no mileage improvements BUT did not like it as much off road. As a matter of fact many guys who purchased ‘79-83’s would immediately regear or swap out to older axles. I wonder if the ‘84-85 4Runner with solid front axle came with 4.10? 3.73 just seems wrong and limits vehicle as to tire size and off road performance.

Gearing can make SUCH a difference. 4.10 seems as though it would be perfect on our T4R’s

CAFE standards.

so i finally got on 285/75r17 nitto ridge grapplers

its slightly slower then with 275/70r17 and less peppy
but i think this is still ok.
4.10s i'd probably jump on for the extra pep

4.56 maybe too much.

i do have a supercharger installed.

How are you liking the supercharger (probably a dumb question)?

Also, would be curious if someone on here with 4.56 gears could throw on stock tires and give us a 60 and 75mph rpm check? Wonder what the MPG hit would be with 255/75r17 tires. All the questions I have are what makes it hard to pull the trigger on gears even though I think that's all I need. The supercharger I know exactly what I'm getting a d it's easier to rationalize what the feel will be. Basically the same tons and fuel economy I have now with the opportunity to put the peddle down for an extra 80 ponies and torque.