PB Blaster and BFH.
If it is as bad as the one on my boss's old 96 Suburban, forget about removing it. He put one in his hitch and installed a lock on it at the same time. 12 years later we tried to pull it out when we sold the burb to an employee. After repeated attempts with everything we had from PB Blaster to Oxy/Ace Torch, BFH, RBFH, we just stuck the lock back in and said here you go.
Soak it down with PB blaster let it sit for a while. Reapply the PB a couple of times. Then start working it over with a hammer. Side to side, hit it on the front. It should come loose. No guarantees.
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