(I did this after completed main game 100% and loaded that save on NEW GAME+ MODE with easy or normal difficulty, so all weapons and skills will be unlocked and easy place to grind. it took 5 minutes to hunt 6 cumulative achievements) For Sixth Sense Achievement, At COZUMEL, after picking up the dagger and you'll come through one enemy near elevator and 3 enemies in beginning of the stealth sequence.. after that you'll jump into a new area where 3 enemies in ground and another one on top of the ruin. So game auto saves here.. with lara hiding on bushes... Now Press & Hold
and Press
to Select Perception and kill those 4 enemies with any weapon before perception time runs out. Repeat this until achievement unlocks, achievement will unlock after killing two enemies on 3rd time.
You'll Unlock
also you can unlock other 5 achievements here...