Not sure this has been asked and answered before. If it has then point me in the right direction.

So here's the deal. I have a 3" lift with oem sway bars. I get a lot of swaying/drift on the highway. So much so that it requires constant attention. I believe my sway bars are too dainty to handle the lift, larger tires and increased load.

I can handle it but my wife hates it.

Has anyone upgraded to a heavy duty rear sway bar? Or did you replace both front and rear? If you did, any improvements on highway handling?

What brand did you purchase?

Thanks.

When you lifted your 4runner, you changed the geometry of the sway bars. The fixes for the front and rear are different and don’t require beefier sway bars.

I bought a Toytec “front sway bar relocate kit” to lower my front sway bar, and put 3rd gen sway bar end links on the rear. I’m still using the OEM sway bars front and rear. So far, so good on my 4th gen.

I'd also do a quick check of all the bushings throughout the suspension. Loose ball joints, tie rods, and control arm bushings can all have a significant impact too.

How's your alignment? Did you replace the upper control arms and add extra caster as is usually recommended for 3" lifts on the 4runner? That can also help quite a bit with stability.

your sway bars have nothing to do with the way it tracks on the highway, they will only come into play under side loading, and while yes, the geometry is off from factory, that is not the issue.

It is more than likely almost fully caused by alignment, in particular not enough caster to keep the wheels tracking straight. If you are on factory upper control arms it's not surprising since you'll run out of necessary caster adjustment pretty quick. Worn bushings all around don't help, and could possibly attribute to the problem, but I don't would be the cause of what you're seeing. My money is on toe and caster adjustment.

If you care to rule out the beefier sway bar theory, take off your links and go for a straight line drive on the highway to confirm is wanders just as much but not more.

Oh, and also, not that this should make it wander too much, but if you're at a true 3" lift and don't have the panhard bar correction kit to re-center your rear axles you probably have it pushed out an inch or so more on the passenger side vs driver side. Not likely to be super noticeable, but you're probably dog-tracking just a bit without it.

longer rear links to get the bar back to parallel, yes, 100% aligned with that.
The front relocation kits though aren't (as far as I know) meant to correct the geometry but rather push the bar forward out of the way of aftermarket coilovers. Physical position (front/back or high/low) of the bar is less of a factor than getting the correct length links to get the bar parallel at ride height to be more aligned with factory geometry

This is why skyjacker lift kits are the sh!t. They build their kits specifically for your truck and to keep OEM geometry for a dang good price. My 3" lift came with rear extended sway bar end links, upper control arms!, and a differential drop. All to keep geometry on point. Front sway is completely factory. Went in for a free alignment check after and everything was perfect except toe from the lift. I was toed in a little which was an easy fix for me. Castor was exactly the same as OEM spec thanks to the upper control arms which also gave more tire clearance at the body mount. I didn't even have to touch the lower control arm alignment tabs. I did the body mount chop for full flex off-road and with 2" spacers I had to do it. I have 33s and she drives like a sports car on corners and drives straight as can be. That is with 2" wheel spacers. Without wheel spacers the factory upper arm would have rubbed the inner tire or come very close with stock rims also. I love the extra width off road also, until I can long travel her 3.5" out. When I first put on my 33s after lift I pulled out to drive home and was really sad how she was cornering. I soon realized the higher sidewalls required more air pressure to stiffen them. It took me awhile to dial in the tire pressure to 42 psi and boom I'm very pleased again. Your castor and toe are most likely causing your drift and eating up your tires. The front sway bar is there for cornering stabilization. Hopefully there's room for adjustment with your castor. There's not much adjustability via lower arms.

^^^ This, front-end alignment (caster/camber/toe-in)

That's sick 😲! I've been in the forest off roading my b1tch hArd for almost ten years. My welder paint reference marks on my alignment tabs haven't budged in ten years. Pretty surprising. I want 3.5" long travel! I wish I had an extra set of OEM lower control arms to play with to add a 3.5" section into. 👽

3" lift?
1. You've lost a lot of caster adjustment. You need aftermarket upper control arms with more positive caster angle built into the design.
2. as mentioned, your sway bars are at steeper angles now so they won't counteract as much sway/body roll. You need longer end links.
3. Did you get it aligned after the lift? If not, as mentioned, you'll need to have camber and toe fixed also.

Hey I know it's been a while, but I'm considering upgrading my sway bars on my 2018 for the same reasons.. did you ever go through with an upgrade and did it yield any benefits?

Get the caster up to 3 degrees or more and it will drive straight down the road without all that terrible wandering.