Ok well it's almost surely front since it's affected by steep steering angles.
Unplug one at a time and see if the problem vanishes. You'll get a bunch of death and destruction dash lights (because, you see, no one ever survived before ABS and TC) but so what.
Or unplug power to ABS pump, but it may be a throttle reduction issue more than a brake application issue. I don't know if TC will still try to work if it knows ABS is disabled, but probably not. Toyota disables TC for seemingly any problem, including not being able to see engine temp, bad MAF, etc
edit: in hindsight "unplugging one at a time" won't expose the problematic side because the system will panic and disable everything. Regardless, unplugging a WSS will tell you if you're barking up the wrong tree. Maybe the problem is something else entirely