Finally found a willing CPA to consult and my tax bill went from 27.9% down to 10.8%. Sure it ended up costing me $300, but I saved nearly $10k.
The CPA stated unequivocally that having used TurboTax herself, it can make many errors - she does not trust it. I don't know about you, but I don't dabble in tax law as a hobby, so all I knew was 27.9% was insane at the bracket I'd wrestled myself into. While she found the offending line item, I researched what had gone so horribly wrong:
W2 Box 12(b) appears as line item 60(c) under Other Taxes, with the code "UT" which is Uncollected Social Security & Medicare Tax on Tips or Group Term Life Insurance. This TOTAL AMOUNT WAS ADDED to my tax bill. Not only was the amount supposed to only be 6.65% of the amount, it was only applicable if reported as codes "A-B,M-N." Mine was listed as code, "D" which is Elective deferrals to a section 401(k) cash or deferred arrangement, which isn't even applicable.