Ok, so a bit more info.It only happens in first gear. Its very rhythmic as seen here. The drive train still turns up to the differential, but after that the wheels lurch like you see in the video. I've disconnected the battery for things to reset and it had no effect. I should note that this started right after the first heavy rain we have had in the area for about a year or so. It may be coincidence. I thought maybe it had to do with me using the winter/wet mode and switching back to standard. I feel like its relevant because to my understanding, winter/wet mode omits first gear, which is the gear that seems to be having issues. I am at 101,000 miles approximately. Fluid was changed not too long ago, just before I bought it at 78k miles I believe.