Tough call. My old 'custom' unit that had the homemade input gear for the custom adapter was pretty dang noisy.
My new case, I just got done building, with all oem/spicer parts is surprisingly quiet. I can still hear it, but it is WAY better than I ever thought it could be.
What kind of speeds are you running? I don't think these old transfer cases are designed to run super high speeds on the road. I think about 50-60 is their happy speed in the long term.
If the stock gears made a huge difference over the Tera gears that is probably the tera gears fault. I would have thought that the new Tera gears would have been quieter than stock? I don't think Tera would have sent you another complete set of gears if they didn't know the gears could be a problem.
42 MB, 225, T18, big kid go cart with clown tires
92 Dodge W250 daily driver on 39s