Chris,
While the starter is out, make sure you change the bushing that is pressed
into the transmission. The starters I have purchased always came with a new
one. A few time I was tempted to say "the heck with it" because it can be
awkward to get out. If you use an Easy-Out it should come out fairly easy.
Who knows, a bad bushing might be part of the problem.

Good Luck,
Ken Lewis
http://neksiwel.20m.com/