I got a new to me truck with the 6L80 transmission, runs great except has a VERY hard shift from 4-5, I'm a BMW tech so familiar with mechanics in general but don't have much knowledge on the 6L80. I already dropped the valve body and rebuilt the seals with the sonnax kit but unfortunately that didn't help at all. I don't think the actual clutches are bad because usually when the clutches are bad the tranny will slip, hard shifting is typically an issue with pressure. I also got the codes P0842 and P0877 for transmission fluid pressure circuit low voltage for switch 1 and 4. Any idea what the cause of the issue is or where to look?