dmertz I think I found the problem - I was double-counting the rollover basis from my employer's retirement plan. When TurboTax asked me to enter my IRA basis on 12/31/2022, I included my retirement lump sum plus the sum of my non-deductible contributions over the years. Then I typed in the lump sum again when TurboTax asked me about the net rollover basis thinking TurboTax would subtract the two. That's why form 8606 box 2 looked suspiciously large.
Suggestion: when TurboTax asks for the IRA basis, include additional wording to remind the user to exclude a rollover basis from employer retirement plans.
The lump sum is no longer double-counted, the taxable amount (form 8606 box 15c) is no longer zero, and my refund is now tame. Fortunately, this was caught by you and the community in the first year I withdrew cash from my Traditional IRA. Folks at the IRS are probably going to chuckle over my explanation that I had to type because of my PEBKAC error. Thank you, dmertz, and the community VERY MUCH for your help!
PEBKAC = Problem Exists Between Keyboard and Chair
