The longer the board, the more difficult it is to keep the plane in a constant motion... you run out of "room".
If you can keep your boards under 24" that would help.
You plane iron may be set too deep and you are using too much effort and thereby twisting it a bit. I think 1/32" is still too much, but over what distance?
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)