Update again: This didn't fix anything, the truck is barely drivable. Gear indicator lights turn on and off, and it just randomly picks the wrong gear to be in all of the time, including neutral sometimes. I thought it might be moisture related, but it's been 80s and 90s this week, dry as a bone and it barely made it across town. Anyone have any ideas? The swapped relay is clattering away like a maniac, same as the previous one, so it's whatever controls that relay that I believe is causing the issue.