Rendering problems

[Rakachu]

sometimes the game bombards me with rendering errors and its getting a bit too much.
this never happened in my old world (which got corrupted).
i always played the pack with 4gbs of ram so i though that was the problem but when i allocated even more ram the problem just got worse. so i went back to 4gbs and reinstalled java and it seemed to work pretty well until i started to venture away from loaded chunks, and the problem got even worse when i got to the beneath dimension.
the most frequent error is rendering in endstone instead of iron ore or dense iron ore.
some chunks appear to be out of place too (some chunks are elevated like 10 blocks)