Added data points:
1. I eliminated my under-withholding penalty
2. Adding a $1000 IRA withdrawal increases my federal tax due by $370
3. Instead, adding a $10,000 IRA withdrawal increases my federal tax due by $3700
4. TT shows my AMT is $0.
My AGI is still far below the 37% tax bracket floor, so it looks to me as if TT is using the wrong tax calculation. I hope that is not true, but I have no other explanation at this time.
