I had same thing except either left or right side too high in the past. The recent bed tramming I did was about 1-2 month ago, gone quite to the extreme method of doing 5 passes to ensure bed are perfectly leveled and measured with piece of paper.
I would recommend use the guide from reprap wiki on how to adjust your bed level. Basically best way to do it is by adjusting screws diagonally, first diagonal would be front left with rear right, and second diagonals would be rear left and front right.
Probably you should try to add auto bed leveling
My main problem I always have is the height of bed. People kept telling me to solve the problem, yet it kept coming again and again. I've been adjusting z home offset (this is overall, not specific point) so I don't have to adjust the endstop trigger