The 5000 lbs rated receiver has 4-6 fasteners attaching it to a single cross member. The factory hitch uses those same fasteners and 4-6 more that attach to the frame rails running length wise along the frame. Thus spreading the load over a more substantially stronger structure. My fastener count is probably off but for sure more than the 5000 lbs rated receiver.
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I bought this hitch on Amazon. It’s a factory hitch sold by a Lexus dealer out of Arizona and comes with all the fasteners and 7 pin relocation bracket.
Installation is pretty straight forward and easy.
Installation pics start on post 72.
forum.ih8mud.com
Think of it this way. Your neighbor runs there crossover into a snow bank, it weighs 4500 lbs. with mire factor (slope angle, snow depth, suction of snow on the bottom of the vehicle) you could easily exceed the 5k.