Pete 387 automatic transmission issues

Hi everyone, I’m new to the forum but have been an owner op for some years now. Been driving my 2010 Peterbilt 387 with a Cummins isx and an automatic Eaton fuller transmission for 3 years now. The truck has been really good to me and thankfully has never left my stranded on the side of the road. My biggest issue I’ve had with the truck since I bought has been the transmission though. For some reason the gears don’t seem to go in smoothly all the time especially when down shifting on the lower gears. It goes into neutral on its own after 6th and will go into the correct gear by accelerating it, the problem is that I hear a really loud scratching/cracking noise when I do that almost like it’s forcing the gear in. I really enjoy the auto transmission but that’s one issue I haven’t been able to fix.

I’ve already replaced the clutch 2 times, wiring harness, all the sensors, XY shifter and another component that I can’t remember the name that goes on the bottom of the transmission. Anyone know what my issue can be?

 

I replaced all the sensors already. I’m not sure if I missed one but there is another one that has a small air line to it. Could it be that valve that’s causing issues?

 

I haven’t replaced that regulator but had heard about something like that. That could potentially be my issue. I’m pretty sure that’s the last external part that would need to be replaced so thank you for that! As for the oil, it hasn’t been changed. I’ll have to ask my mechanic about it see what he recommends. I made the mistake of taking it to someone else the first time I replaced the clutch and they did a crappy job since it started slipping soon after.

Thanks everyone for the help! I will update once I replaced the regulator as filter