I have heard of this problem before but dont remember what was said about it. My 97 vibrates at around 55. I have had the balance done and I rotate tires on schedule. I have heard getting a centerfugel tire balance done and if that doesnt do it then it is the ????????????. Does anyone know what I am talking about. I think it said something about the camber but I dont remember.
Its a 4WD if that makes a diffrence.

 

Make sure the alignment is OK and that the lugs are torqued to the correct specifications. It's 83 ft. lbs. for a Taco, not sure what it is for a 4Runner... I would think it would be similar.

 

What about the hub/lug centric balancer?
They might have use hub centric balancing when it is lug centric.
Does that maybe help?
Just trying.

edit:
Also, I had a problem like this on a work truck. Turned out to be the steel radial in it was messed up. It would only do it at a certain speed. Faster or slower and it wouldn't be there.
I don't know if that makes sense, but the tire was shot basically.

 

toyotas use a lug centric design, not hub centric, if the hub centric is what most balancers use, it might not balance it perfectly... however, perfectly with any balance is impossible, it can almost never be 100% perfectly balanced...