Ah, could be I done them as tight as I could (hand tightness) but today I done this on the rear diff and it's as smooth as silk :/. I'll re-do the front without doing them up so tight, see if that helps.

Dawman, I don't think it's the internal gears (inside housing) as it doesn't matter when I hold the outside still and rotate both axles (very smooth). The outside gears are the same as what was in there before, just cleaned and greased up again.