Sudden Movement... Let me explain

Evening All,

I have played PR for many years but have had a break of about of 2 years, i used to run the game smoothly on a fairly low spec PC, i now have a fairly beefy PC yet during gameplay it will without warning give a short sharp dose of lag and send me in any direction, this of course makes flying completely unsafe. Can any one advise why it does this, is it a bug with the latest patch?

Thanks