Front & Rear Differential Factory Fill Low

The spec is pretty generous, +/- 5mm of the fill hole level. 5mm depth over the entire width of the axle tube can be quite a bit. Spec has been that way for the last 15 years. It has a negligible effect on cooling the rear diff. That's about it. The smoothness you perceived (assuming it isn't placebo effect) would be from the better Redline fluid, not from the fluid level.

 

Unless the truck has been sitting on the lot, then bits and pieces will stick to creases (like around emblems). First hand experience.

 

The rear in my My 2018 TRD pro with 40k miles on it was about 1qt low. The fluid that came out looked practically new. I'm draining the front right now and it looks way dirtier.

 

My 2021 2.7 was 1 quart low at 27k miles as well. Put just less than 4 qts back in before it started coming out the fill hole. Fluid didn't look that great, at least compared to new, and magnet was covered in fine particles. Has me questioning all fluid levels from the factory at this point.

 

My 2.7L early 3rd gen came from the factory almost 1qt low in the rear diff too

 

I keep seeing these comments and that's exactly why I'm going to drain/fill my front/rear at 15K. Saving the transfer case until 30K. There's a lot of people on this forum who say under fills from the factory just never happen and we're all smoking crack. Makes me wonder about other fluid levels from the factory.....you know.....like A/T fluid?

 

Fluids are cheap.
Change the engine, oil, differentials, and transfer case early