Okay so i was having the same issue drove me nutz two hdmi external monitors with big slur brand new laptop... almost went back to a 5 year old laptop,,, the itermittent lagging was pissing me off very annoying... I research and tried all sorts of things like turning the auto switch graphics in battery settings... nothing... so i was about to wipe this thing and by habit just turned off all my cloud data backup ,,, pretty much anything to do with the icloud and programs sending / storing data to it i turned off now things are working... who the hell knows hope this helped... no lag.