Judging the APR based solely on your credit score and debt-to-income ratio, 5.99% APR seems a bit high. However, your credit score and debt-to-income ratio may not paint the total picture.
If you have little income and a thin credit profile, 5.99% APR might be great for a car loan. But if you have more income and more credit history, shopping around some more might yield some better results. If you haven’t done so, check out credit unions or online lenders to see if they can beat your current rate.