Have you tried your Shield / Kodi setup on your friends set which you seem to like the motion of ?
That would be my first port of call
I had 2 Shield / Kodi setups for a long time and as good a bit of kit as they are, Kodi was never perfect and no matter how many times peopel tweak and play with the settings they never seem to be right for everything
Have you tried watching one of your movies via another medium / device
So a blu ray version or a version from a legit streaming source ?
How do movies look via Netflix or Prime using the inbuilt apps or apps on another device ?
In short, for now, remove the Shield from the chain and see if the issues are Shield related or TV related
As said before, Ive never seen motion as good on a flat panel as I have on this set so for me it suggests either a fault with your set (possibly unlikely) or its not configured correctly ?
The movies on the HDD, are they "legit" - have you ripped them yourself from disc ?
If so how does that same disc look when played back ?
Not judgning but remember movies streamed from the various Kodi addons or downloaded via non legit means are obviously not 1:1 copies and again this may lead to issues ?
Finally have you downloaded the framerate utility for the shield as previously mentioned and covered here in the shield thread ?