When you "traded" for the new property you deferred the gain on the sale of the old property. Because the gain is deferred, your basis in the property acquired is reduced by the gain that was deferred. That information should have appeared on your Form 8824 (link below)
Example old property cost 50,000 depreciation taken 20,000, fair market value 80,000 at date of trade. New property 100,000 value at trade, 5,000 depreciation taken, value today 120,000.
Your basis in the new property is 45,000. Adjusted basis in old (50,000 - 20,000) plus cash paid 20,000, less depreciation taken on new 5,000.
Sale of new property your gain is 75,000 (120,000 - 45,000) of that gain 25,000 (20,000 + 5000) is taxed as real estate depreciation recapture at 25% the balance of the gain 50,000 (75,000 - 25,000) is long term capital gain.