sale of vehicle used 10% for rental properties

If I purchase a vehicle for $34k and sell it for $15k and used it 10% for rental properties.  I took at most $2k in mileage deductions over 4 years.  How do I enter this?  It keeps saying I have a gain.  If I lost $1.9k (10% of loss) and part of the $2k was reimbursement for spending on things like gas, oil changes and other consumable items that I spent money on in addition to the $34k, why do I have a gain?  Do I need to add gas and maintenance to the purchase price.  Do I ever answer the questions with a negative number?  I didn't depreciate the vehicle and it asks for a depreciation type and year.  The questions are never ending and it seems like the mileage rate was just offsetting actual costs.  Is it better to do actual costs instead of the mileage rate for a vehicle used 10% for business?   It feels like it is making it more complicated than necessary.