Writing a letter to my pastor

[Real Realism]

If you are at peace with the decision to leave, despite the outcome of the conversation, I agree with Ferd that it would be prudent to skip the "negative" and be as gracious as possible.

Unless you're content with the likelihood of your pastor taking your leaving as a result of his stance on tithing and not reengaging with you upon your return - I wouldn't mention them. No matter how kindly you try to broach the subjects and ask him to clarify his stance - mentioning those issues in the same breath as saying, "Pastor, I feel led to move on to a church in a town that's part of my sphere of influence." - He's only going to latch on to the negative reasons. No fault to him, IMO, but that's just human nature.

If it's more important for you to clear the air with him before you move on, then by all means, have the conversation. But just know what the consequences are likely to be.