There’s a blue or green color(I forget) think it’s a blue relay on the fuse panel on the driver side kick panel. Should have a number on back. It does weird shit. It’s a turn signal/flasher relay napa# FC6530 see if it matches yours. I had to get genuine a while back cause it’s a special type and my truck didn’t like copy cat relays. But that Napa one should work fine. If you got your old one off, see if it has part# 68499015AA or 56007348. Supposedly, that first set of numbers replaces the second. My truck is same as yours without the electric seats.and not as beautiful as yours. That relay gave me and customers problems. I did the same replaced multi function switch too but relay was the culprit. Hopefully it works for you.

Unplug you tail lights and parking lights. I was thinking maybe a bulb filament is burnt and dropped on to the other filament (shared ground) that would connect 2 circuits through the ground.