Those might be stuck in pretty good, might be more than even a bigger skidsteer can pull. If the ground is firm enough to get a forklift in, you can get a lot more pulling power by getting right up on the mast. Also, when you're at the end of the line, you can spread the forks and load up the posts on the way back. I know; I've got a forklift, so that's my go to. When you have a hammer everything looks like a nail.