I have replaced all tail light bulbs with 3057 bulbs which are supposed to be the correct bulbs. I kept replacing the fuse with the standard 20 amp I have even tried over-fusing with 30 amp fuses. The tail lights will stay on from 2 - 20 minutes just depends.
Please check all your grounds. There should be one at the rear of the car along the frame rail. Does it have a trailer wiring harness? Ive seen those cause major issues and its the last thing people check.