Without looking at your tax return, I cannot give you an accurate reply to your question.
However, I can see one main reason. The interest reported in box 3 of your form 1099-INT is subject to the Net Investment Income Tax (NIIT) of 3.8%, on top of your income tax at the marginal rate of 35%.
Please read this IRS document for more information.
Also, certain tax credits may have changed with the increase of your AGI.
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