I am having lag issue on games

Kong

 Games that have a driving component such as GTA and Watchdogs may run smooth while on foot, but suffer lag when driving due to the quicker pace of scenery loading.  Some games have a specific setting that will hammer fps. You can often find out which on a forum for that game. Depending on the game and how often it loads scenery or levels I think there is some potential for lag with a HDD. A lot of recent games gorge on memory so much that they are also affected by the rpm of HDDs. Trying moving the game to SSD, if you have one installed.

 If the lag is visible in frame rate drops and V-sync does not help, try enabling triple buffering, or lower a setting or three. Start with reducing Anti-aliasing, if you have it enabled, or disable AA altogether and use FXAA. 
But going through threads fot Watchdogs and GTAV,  and it was apparent there are a lot of people having stutter issues with this game. Nothing unusual though. I've seen countless threads relating to stutter/micro-stutter/stammer over the past couple of years, and with almost every high spec game released. It can be difficult to source the true cause, so it comes down to reading threads about the problem and finding a fix that works for you. There is no one size fits all fix.
Also try the following link which has some resolution for GTA 5 lag/stutter: