I have one more suggestion which you can try; then I'm out of guesses.
It's a feature called pre-rendered frames.
Your card should support it.
Open up your NVIDIA Control Panel, navigate to 3D Settings->Manage 3D Settings.
Go to 'Program Settings' and select the game in the drop-down menu (if it's not there, you can create a new game profile as you don't want to apply this change globally).
Scroll to 'Maximum pre-rendered frames' and override the global default (usually 3) and set it to '1'.
Scroll further down and make sure 'Virtual Reality pre-rendered frames' is set to 1; it should be by default.
Apply the changes, and try again.
Some people have seen drastic FPS increases by doing this; others have seen FPS drops, and others more have seen no change.
I'm sorry I can't help further.
~ NuttiKrust
I tried your first suggestion, it didnt work so well, but i noticed the problem. The lag and stuck happen when its rendering/processing a lot of texture. When I wait at the screen to load for a long time, the lag reduced because its already rendered/processed the texture. Same goes if I went this specific path, next time I cross it, the lag will gone because the texture has been memorised. Do you guys know how to counter this? Thank you