Lagging issues?!

I am using an MXQ Pro Box. Upgraded internet speed to 200 mbps and this has helped. I have also tried adjusting some different advanced settings. The movies we watch no longer stop to buffer any more but we experience a lag with the audio and visuals after a few minutes. It is driving me crazy. I have read through some of these threads and have googled a ton of stuff but nothing I do seems to help. Can anyone help?! Much thanks in advance