The original question asks about what trucks are available and at what dealerships. The edit alters the accepted answer by updating with new dealerships and I assume new trucks.
Is updating someones answer to include new content correct? I would assume that it is not. You are now changing the content of someones post. If you change it to something that is now wrong, you draw downvotes to that post that the original poster might not deserve. I would think that the correct action is to post a new answer and point out that your answer details content added by DLC.