If the puller is big enough to take the punishment, I´ve had pretty good luck, in tightening things to the point of bursting, then hitting the end of the threaded (puller) shaft with a BFH (I have kind of a super duty puller). And/Or wacking the side of the pitman arm, the part that the sector shaft goes through, on the side with a BFH, which may be kind of hard on the sector shaft, but sometimes you got to do, what you got to do.
I have an assortment of hammer metal wedges that I actually use for body work, but have found when all else fails, a wedge of about the right proportions and a BFH, will move things a puller sometimes won´t. A large cold chisel wedged between the box and the pitman arm, might get things moving, will probably mess up the box, but probably won´t hurt the arm any more, than a little file work won´t fix.