Taillights work sometimes. Brake lights not at all.

[95gmc]

Yesterday I drove my truck a little bit noticed that the left blinker was blinking fast, just figured a burnt bulb I got home and my girlfriend was following me and said I had no brake lights but the third brake light worked, license plate lights work. One blinker works. I turned the parking lights on and it took about 5seconds for the taillights to come on then they shut off. I haven't had much time to mess with it, but has anyone ever had this problem? Where do I start? Truck is a 98 Silverado z71. Thank you in advance.