when you say TT printed out vouchers for 41k was that generated when you did your actual 2024 return, or when you did the experiment return for your 2025 numbers?
when you did your actual 2024 return, by default TT will use the "100% of 2024 tax" (110% if AGI > 150k) and assumes your 2025 withholding is the same as 2024 (so if using those amounts check the withholding assumptions if applicable). You can also then go thru "Other Tax Situations / Form W4 and Estimated Taxes" and give it 2025 estimates, in case 90% of 2025 tax is lower.
If you are looking at ES vouchers from your experimenting including the 2025 cap gain entered as tho it was 2024, it's generating vouchers for 2025 probably based on 110% of the experimental tax which was entered as tho it was 2024, as presumably your AGI will be > 150k in this case. That's probably why the vouchers say 41k but the tax is 37k. The tax from your experiment is a good benchmark for your final return (bear in mind some deduction limits or tax tables will be different for 2025), but ignore ES vouchers generated by that experiment.
In your situation if you expect a significant income event in 2025, you can pay ES based on 100/110% of your 2024 tax which should be significantly lower (and check withholding in that calculation). You will owe the balance in April 2026, but you can earn 4% interest in the meantime. It also won't matter how much the 2025 income is or when it occurs, as long as you are paying ES quarterly based on 2024 you are protected.
If you didn't make Q1 ES or underpaid, make sure to catch it up in Q2 by paying 50% of the total ES by Q2. You will still have a penalty for Q1 but it will stop the penalty accruing for more than a few months.
