Did you buy this vehicle used ,cause I know there when the daytime running lights first came out ,for certain vehicles ,certain companies selling a kit to keep the daytime running lights on even when you had the headlights turned on ,which basically bypassed the override mode or someone could've rewired the lights to do that as well . Probably the best thing to do is find out if the emrgency brake will keep the DTR lights off ,go start your truck with the emergency brake on and check to make sure they are off ,if not then it is possible the lights have been rewired then check the fuse to make sure they will go out that way then if they do turn on your headlights and make sure they are working properly as well , when you find out what the problem is post back so we can see what the fix was . Good Luck