I had the same problem on both of my trucks. Turns out it was my passenger side clear corner. If I unhook it I have no problems. I don't know if its the socket or the bulb sitting in it crooked though.
I had problems with the tails on kermit. Ended up being corrosion on the harness plugs into the tail light housings,and I sanded down the grounds on the frame under the bed and never had another problem.