If your income was high enough to be hit with AMT, you would have a different basis. If you ever had form 6251 as part of your return, you may have been hit with AMT. The worksheets for depreciation would have the normal and the AMT. The AMT would have reduced the amount of depreciation allowed at the time. You can have it back now that you are disposing of the property.
Some people saw a credit for prior year AMT paid last year.
If you have/ had a six figure income during the time the vehicle was claimed, double check your returns for 6251 and depreciation worksheets.
If you don't have AMT, the basis is the same for regular and AMT.