When i start the game or fast travel i often see very low res textures which are replaced with high res ones after a while

I have 2x SSDs in raid 0 config which i have bench marked and they have very fast read speeds (around double the average SSD speed)
I have a 780gtx with 3gb gddr5
and 8gb ram

So data access speed and storage cant be the problem
the only thing i can think of is that my system ram is slow (its one of the slower types of DDR3), but i would not expect this to be an issue because textures are stored in video ram

any suggestions.