About a month ago I threw on a whole lift kit along with 285/70/17s on my 2001 4runner. Everything was feeling smooth and wasn't noticing any problems until one night out of nowhere, about 2 weeks ago, my RPMs shot up while driving and I could no longer move. Cant get it into gear besides park.
Took it to the shop thinking it was a transmission issue but they came back today and let me know that it is a front and rear differential issue. They told me that the bigger wheels and tires with stock gearing really put load on the diffs, so they gave me a new shop to call and also said if I stuck with stock gearing it would go bad again.
My question is, how many of you here run stock gearing with this tire size? I was looking around the forums a bit and saw that people did this same type of upgrades but was able to stay stock gearing with no problems.
Should I re-gear, and if so, what would you guys suggest going with? Note: this is my daily driver with plans to wheel it on the weekends from time to time.

Any input is appreciated. Thanks!

Get a 2nd opinion. There are people running 35's on stock gears for over a decade. Sounds more like a transmission issue to me. Very unlikely the FRONT and REAR diff went out at the same time. You would hear some horrible noises when the rear diff lets go.

Thanks for the input. When it first happened I thought it was a transmission issue as well so that's why I took it to the shop but they said it was the rear diff so that made me happy. Sure hope its not the trans cause I was having trouble finding a remanufactured trans/a fair priced trans rebuild shop... Think I am going to have it towed back home and drain the diff fluid to see what it looks like and hopefully find my problem..

+1 on 2nd opinion. It would be a miracle to sheer both ring gears at the same exact time from on-road driving, and as said you wouldn't heard/felt it. In fact I would like to know how they determined the front diff was damaged too if it wasn't engaged.
Technically you want 4.56s for 33in tires - but 4.10s can handle them just fine. I would say out of all the 4Runner owners who had 4.10s and jumped to 33s, maybe 10-15% have regeared as well.

Yeah that is a good point... how did they come to conclusion that the front was damaged when it wasn't even engaged. I think I will stick with stock gearing.
Going to get it towed back home soon, drain it, and if it is just the rear diff, will just get a new one from east coast gear supply.

Thanks!

I have 4.30's and 31s. I would hesitate to say that 33's and 4.30's are the sweet spot.

4.56 would honestly be better. I can't even go up the smallest overpasses without downshifting with these 31s. Although I did have a broken spark plug wire for who knows how long.....

I can't imagine 33s with my current 4.30 gearing. I'm going to 4.88 when I step up to 35's and even that is probably on the edge of what's really needed.

Oh yeah duh, I meant 4.56 4.30 was already offered for the car

I’ve had my 285/70/17 for four years, do a lot of highway miles besides local driving and some Offroad parks and trails - never regeared.

u say out of the "no where," No issues like trans slipping or anything like said? Tcase Hi/Low moving in and out normally but still wont engage? Reverse Work? removed the Driveshafts and lift the rear/front and turn diffs/tcase by hand?? like stated by others HIGHLY doubt the shop is correct or even has a clue, U ask them to explain what they did to determine their diagnosis?

Sounds like Trans issues, U pull the drain and look at the fluid? thats where i'd start...

Yeah, seriously was out of no where.. I drove it for about a week and a half with absolutely no issues presenting themselves other than some sway in the rear since I dont have the panhard bar at the correct angle yet. Did not hear any weird noises or rough gear shifts, it actually felt really smooth.

I did not ask the shop how they came to their diagnosis, would've been a good one to ask about, think I will give them a call back and ask about it. Reverse doesnt work either, it will not go into gear at all, it just makes grinding noises.. only goes into park and neutral.

The night of the incident I checked the trans fluid and it looked good.. red in color and was at the right mark. I am going to drain the diff once it gets towed back to my house and will give an update here once I do. I really hope its not a trans issue but if it is, you got places I can start looking for a new trans?