Given correct input, TurboTax does calculate the maximum SEP contribution correctly. Examine TurboTax's Keogh, SEP and SIMPLE Contribution Worksheet. Perhaps you have also marked the Maximize box for an individual 401(k) contribution or you have somehow incorrectly entered your self-employment income. The maximum permissible SEP contribution is 20% of net earnings. Net earnings are net profit minus the deductible portion of self-employment taxes. If your only self-employment income is the ~$76k, your maximum SEP contribution is ~$14,100.
I'm not sure how a Schedule K-1 would have anything to do with your self-employment income unless it was from a partnership that is separate from your other self-employment income. If it's from a partnership, there is an amount in box 14 with code A, and you have separate self-employment income from a separate business, there are likely additional restrictions on how much you can contribute to a SEP IRA.
