Just wanted to introduce myself since I'm new here. I own a 09 taco. Also have a 94 & 95 4 runners. I've been a mechanic for about 35 years and I love all things Toyota. Live in Texas,north of Dallas about 90 miles.
I've used Coopers for about 35 years. I've currently got Coopers on two 4 runners and my taco and my wife's hyundai. I've never had a separation problem or balancing problem with Coopers. And they actually wear pretty good.
You've got a balance problem. if you feel it in the steering wheel its one or both of your front tires, if you feel it in the seat of your pants its your rear tires. I've been a mechanic for 35 years. some tires are just hard to balance. And it could also be the idiot balancing them.