Sounds like you are having other issues, If it is harder in 1st and 2nd you have a release issue with the clutch itself or a hydraulic problem not allowing the clutch to completely release. Fluid won't cause hard shift issues normally and if it is a little thicker fluid it will only do it cold.

 

I finally did JWT clutch kit install and oil change in gearbox and diff. After bleeding out the system, I can't feel any difference in pressing the clutch pedal before and after, it might be even softer than it was with stock clutch kit.

Shifts are much smoother now, but that happen after gear stick alignment, mine was just a mm or less off, but it made a huge difference! You should check yours.

No gearbox chattering at all, although I have slightly higher idle (750 rpm) and I really take some time to smooth AFR around idle, so there are almost zero engine vibrations/shaking.

It revs much easier now

 

nice nice ! i love mine too. It will chatter more once you break it in.
my pedal was stiff as he** when i got it first installed. Now it got little bit softer but still stiffer than the stock.
How do you go about doing the gear stick alignment?

 

Here's a DIY, it's very simple to do.