Gear ratio dilemma
 

I have been toying around with the Idea of regearing my 87 4runner 5spd 22re so I started looking into what gears would be best from what I can tell I want either 4.56 or 4.88. I never plan on running anything bigger than 33s. I started playing around with the gear ratio calculator on Grim Jeeper gear ratio calculator. And noticed that according to my RPM range, 3100-3200 at 70mph, I already have 4.88.... Everything thing about my truck says I should have 4.10s. Ive even jacked up one tire and spun it while watching the driveshaft with tape and in my best estimation it spun just over 4 times which would makes sense for 4.10s but like I said the RPMs are telling a different story. I dont wanna waste time going to a junkyard and pulling diffs out of a auto 2nd gen and swapping mine for no results. I attached some pictures including a photo from a stamping on the actual rear differential. I used tire size as 30 because right now I have worn 31x10.50R15 so the sctual size is probably close to 30. Any input or help is appreciated.
https://cimg3.ibsrv.net/gimg/www.yot...5cd86eee44.jpg
https://cimg5.ibsrv.net/gimg/www.yot...f6e7d69f75.jpg
https://cimg4.ibsrv.net/gimg/www.yot...94ff51408e.jpg
https://cimg6.ibsrv.net/gimg/www.yot...1431a718f8.jpg
https://cimg9.ibsrv.net/gimg/www.yot...e146e48c06.jpg

Your truck has 4.10's

It is easier to note the ratio if you go around twice.

8-9-10 is a lot simpler to notice than is that .1 .5 or .8...

You can not trust the build tag, it could have been altered anywhere between the truck it left the factory on and now.

You can not trust the speedometer, for one they are allowed upto 5% error and more importantly tire size is almost never accurately displayed by manufacturers. To get an accurate tire size you have to measure it's rolling distance and math it out.

watching your driveshaft spin is subjective IMO.

like CO_94_PU said who knows who has done what to the truck over 30+ years

to me the only sure fire way to confirm the ratio is to pull the 3rd, count the ring gear teeth and divide by the pinion teeth

borrow a set of 33's and set how it does

Your speedo is not GPS corrected.

someone correct me if im wrong but im pretty sure Toyota paint marked the pinion for different gear codes, (pink, white, something something darkside) im sure you can find the thread on here somewhere. I aslo know that they wear off a lot so this may not help. I will also tell you that 4.88s with a set of 33s is a good life.

where was that mentioned??

Your truck came stock with 4.10's. Doesn't mean someone hasn't changed them, but I would guess it still has them. You're speedo probably isn't right, a lot of those were set with 225/75r15s from the factory, and that is considerably smaller than 31x10.5s. That being said I am currently driving an 89 that is the third recipient of a set of 4.88s. I run slightly smaller than 33 tires usually (prefereably a metric equivalent to 32x10-10.5, I don't like wider tires) I like them, but on long freeway trip like when I go to Wyoming I will take an hour or two longer than when driving my Tacoma with the 3.4 and stock gears. It doesn't like much over 70-75 mph. I drive the freeway three or four times a year with this truck at most, there isn't one within a hundred miles of me to the north and a couple hundred to the south, so that isn't a real big issue with me, but keep it in mind. If you have to have higher sustained top speeds I would go with a multiple transfer case setup, for driving logging roads (run it in 2L) or wheeling, but frankly these 22re don't have much power before you put bigger tires on them, so if you do much hill driving and/or can accept the lower freeway speeds the 4.88s are the way to go IMO