I ordered up the stuff to make two of these setups.
Pin, shackle and shackle block all made in the USA.
The block says 13k, the pin is 20k+. Is that a 1/2" shackle? If so, it's probably near 20k breaking strength. So, the block is the weak link. If that isn't enough, you likely need a heavier hitch. It's certainly more than the OP's 4Runner can handle.