Business Auto Depreciation

We traded in a business vehicle for a new vehicle.  I entered the sold date and amount of trade in for the old vehicle.  It is showing a gain on the sale of $20k.  When I add the new vehicle I entered the amount paid with the trade ($19k)  and the total purchase price ($39k).  It is taking the full $39k as the first year depreciation even though I entered only $10k in as the section 179 deduction.  Shouldn't I be able to take the depreciation over the 5 year term?