If you used the per-mile method, then you need to recapture the depreciation taken for business miles claimed each year. Hopefully, you kept records. You'll need the depreciation per mile for each tax year, since that changes each year. The table you need for depreciation per mile is just over halfway down the page at https://bradfordtaxinstitute.com/free_resources/irs-mileage-rates.xml.aspx
I seriously doubt you sold or traded in the vehicle at a gain. Even with recaptured depreciation I'd expect you to still have a loss, and a pretty big one most likely. But of course, the oxymoronic rule set may apply here too.
