I've read some good replies so I'll just trow this out.
my Friend's 350 had the hitch rusted stuck after only a couple of months so being the jackasses that the we can be sometimes we chained it to the back of my Chevy 3500 dually and had are ford vs Chevy pull off (four wheel drive in concrete) after a lot of doing back and forth we stopped before we really broke something we had are trucks hopping.
the point is that just jerking it doesn't work very good. so after are fun he just put tension on the chain and i hit the hitch with a BFH and it just came right out. I'm sure you need more than a tap with a BFH but save your truck and don't just try and jerk it out.(it is funny to watch though)

billybee60: after you get it cleaned out put a rag loaded with grease in for the winter. my .02 cents