Over the last few days I've noticed a problem that appears to be getting progressively worse (though it may be that I am simply more aware of it). When using abilities I've noticed a definite delay between when it is triggered and when it actually occurs. This first manifested itself when I noticed my runes behaving weirdly. However, when I moused over my action bars, I realised that the GCD is triggered and about a third completed before the action actually takes place. Also, when playing caster classes, my casts end well before the bar showing when it should (accounting for lag).
As stated in the title, my ms never goes above 25 and my fps is a solid 60 in almost all circumstances (all setting maxed at 1920x1080 apart from shadows which is on high). My first thought was that it was an addon problem, but after trying with all addons disabled, the same issue occurred.
It is becoming increasingly difficult to play properly as I feel my performance is hindered significantly by this, as well as just not feeling 'right'. Any suggestions as to what is causing the problem and how it could be rectified would be deeply appreciated.