remix919

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?

Hey all, it seems I have the infamous service trailer brakes message on my DIC, I got error codes C1112, C1114, and C1119. I checked all the trailer related fuses (1/3//6/10/25) already replaced both the switch in the cab and the relay in the back with new geniune GM / AC Delco parts. I also cleaned the G401 ground which on my truck with the factory tow package that seems to be located above the spare tire mount and not near the back frame rail as all the diagrams show. I did a quick look at the wires and connections I could see and didn't see anything obviously wrong. At this point I'm at a loss, any ideas where else to look? I'm fairly certain the ground is good because I just cleaned it very thoroughly so perhaps I'm thinking I have a short to voltage somewhere?