Vinny mentioned to check the trailer wiring. I second that.
When I got my truck I needed to replace the turn signal switch, one of the tabs that hold the turn signal on was broke.
Afterwards, IIRC, I was also blowing the fuse for the brake lights and my tail lights were intermittent and the license plate lights were not working.
The trailer wiring had been spliced into and wired incorrectly. Ended up getting it all out where I could see it and got the EVTM out and straightened it up, been fine since.
Hope you get this soon, these kind of problems can drive you nuts.