Well I can tell you exactly what it is.......happened to me about 2 months ago. Your door lock mechanism is frozen. You will have to replace it. Cost me $65 shipped if memory serves me correctly. Took about 30 minutes to replace it. The problem is that if you have not changed the way your truck unlocks, meaning 1 click of the key fob unlocks all doors, you have to click the key fob twice to unlock all doors. When you do this, even though you aren't unlocking the drivers door again, you are cycling it just like you would if it was unlocking. Therefore it is getting twice the work out than every other door. It is a very common and it is easy to replace the locking mechanism. Let me know if you have any questions.