Differential catching after fluid change

[Gotterbein]

2018 Power Wagon, 60K service.
Changed the differential fluid, had not performed the trans yet (waiting on parts)
Afterward, getting a grinding/catching/popping feel when leaving from a stop. Worse, when in reverse.
Research is indicating that the rear differential needs a friction modifier added to the fluid.
Dodge/Ram parts and service say that no friction modifier is required. My understanding is that the PW has a Torsen Limited Slip with an E-locker. Torsen has no clutches and shouldn't require a friction modifier.
What's weird, also, is that the rear differential fluid was dark, like clutch material in it.
This problem showed up right after the differential fluid change.
Thanx

[Retired BLM Rig]

I've experienced the same shudder after a fluid change. It's undetectable if you start from a stop in a straight line but if you're turning when you start out, that's when you feel it, indicating that it's related to the differential action happening inside the carrier. After I added friction modifier, it went away. I used high quality fluid but apparently it wasn't rated for limited slip applications.

Welcome to the forum!

[jeep_boy02]

I've got it in mine too. But wasn't till my 3rd diff service which I went with Lucas. Later on found I needed a R&P but after that the shudder was still there and I used Amsoil. It's barely noticeable now unless I have 12k+ pounds towing.

Was exactly same feeling as Abel stated.

What's really odd is you're correct, our LSD are not clutch based and should not need a modifier but I've seen many PW owners say after using a friction modifier it went away.

[RustyPW]

I've always used Mobil 1 gear lube. Never had that shudder.