99 tahoe rear driving lights wont work.

Hello. My rear driving lights seem to work only when they want. Brake lights always work, turn signals always work, only the night driving lights that come on when the headlights are turned on. Ive checked all the fuses under the hood and inside the drivers side door and all check out fine. Also there is no speed flickering on the turn signals that usually happen when a bulb goes out. To recap it is both sides driving lights only. Sometimes they come on after driving a little. I tnought i had tracked it down to only not working after a rain or something but they went out on me last night and it has been dry for a few days. Any help you can give me would be greatly appreciated!