I'm not sure if I have any advice, per se, but I am not submitting a chapter from my thesis. The reason is because my interests have shifted a bit since then. Instead, I plan to discuss in my SOP how my thesis pushed me into the direction of what I am interested in now, and then my writing sample is going to be a conference paper that I presented last year. The conference paper is only 7 1/2 pages long, so I am currently working on adding references to theory, the current conversation about the text, and specific quotes from the text, the kinds of things you cut out for a conference paper.
So, I guess my two cents about whether or not to submit your thesis chapters relates to whether or not it demonstrates the area you are proposing you want to focus on. Pick which one best fits that and put your work into that.