Hmmmm....if only I could get my truck to drive on three wheels...Get a truck rim and place it right upright against the post. Place a chain over the rim and hook to the bottom of the post. Get your vehicle out in the road and pull the chain. The chain will pull up on the post as well as away from the rim and the post will come out of the ground. This works on shrubs too.
Seriously though, great suggestion, just not feasible for me. Wonder if I have something else that would work instead of the wheel. Gonna have to look.