Pinhead's method works. The shaft the Pitman arm is on is tapered and whacking the side of the eye tends to work the arm down the taper. And for those who said to "tap" it with a hammer, forget it! It takes way more than a tap. I soak it in advance with Ole Red, put on and tighten the puller, heat with a propane torch (all I have), whack with a hammer, tighten the puller if possible, heat, whack, tighten, etc. After a few cycles, it will come off. If you get frustrated, soak some more with ole red, tighten the puller and come back the next day.
BTW I ran into a tie rod that was harder to get free than a Pitman arm! Used basically the same procedure and finally got it off. One problem I had was getting my puller to get a good bite. I wound up using a large C clamp across the puller to hold the two arms together. The puller I used was like the one in the second photo of post #6.