that 5500lbs. tow rating is only IF your 4-runner has the factory tow package.
if not, then it's not rated to tow that much.
since it's a small hybrid, i think that, IF the 4-runner has the factory tow package and you get a good WDH with built-in sway control, then you should be fine. a good WDH, with built-in sway control. would be the Equal-i-zer or the Reese Dual-Cam. both are superior to the old technology ones with friction anti-sway bars that have to be disconnected to back up.
of course, the best brake controller would be any of the Prodigy models.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC