we can't see your return or the IRS notice. I don't remember seeing another thread that this issue existed. I don't know how much detail the IRS notice contained but if it did you should compare it to the Turbotax capital gain calculation worksheet and then post more details.
I would think that most likely Turbotax calculated some capital gain as short-term when the iRS calculated it as long-term. This is why AGI and taxable income would not differ, but the tax would. Another possibility is that the Turbotax capital gain tax calculation worksheet had an error at the time you filed but then I would expect to have seen multiple threads that this issue existed.
