Effects from mkv 1080p files causes my tv lagging

[piruett]

Hello, my english isn't that good but i'll try. Since I formatted my PC to windows 7 home, I wanted to view mkv files with an embedded subtitle on my Sony Bravia KDL-55HX855 and it works great with PMS. I have only one problem with mkv 1080p files that lags, but not all the time. If I open Avatar, it runs perfectly until some scenes that got effects causes my tv to lag, like a bad graphic card that can't handle it. The same as the movie Transformerd the third. I was thinking it could be wireless so I plug with a cable from tv to the modem, it still lags. Then I plug the cable to PC instead, it still lags.

My PC should run mkv 1080p files very good:
Intel CPU 3.30 GHz
16 GB ram memory
Nvidia Geforde GTX 580
100/10 Mbit ISP
1 GB network card

Can anyone help me to fix this issue? Thanks!

Edit: I used a program Serviio just to see if the lag is still there but it's not. It has no lag at all, so it's something wrong with PMS with default settings. I don't want to use Serviio because it doesn't support subtitles.