Mkv playback problems

When playing back MKV files i find that the picture especially on busy scenes i.e. forests and city views the  picture becomes quite stuttery and no longer smooth . I have a gen 3 HD TVLIVE … My files are usually 4gb 720p ones , they are connected to my box via a 500gb external hardrive … my tv is a Sony KDL-EX503 , i have set the motionflow to off, standard and high but im experiencing the same results… i have set the framerate of the WDbox to auto … I have also started to run the file through HANDBRAKE to see if this helps , but im not confident… Im running the latest firmware 1.09 and I am still getting the odd reboot during playback ( I had hoped the latest firmware would cure this ) …I am very happy that the streamer has played every file I’ve thrown at it but this issue  is beginning to annoy me …I am thinking of buying the cheaper Sumvision Cyclone 3 media player to see if this  will solve this motion problem , or am I doing something wrong with the WD set up…any advice would be gratefully recieved …thanks in advance…

Try posting in the correct forum. This forum is for the 2010 model.