2D Character jittering after build. (Unity 5)

I'm making a 2D platformer with a rigidbody2D character that the player controls. The horizontal movement is handled by translate while jumping is handled by the velocity.y of the rigidbody2D. The character acts normal when in the editor, however after building the game it starts acting odd. If I jump up and the character is just moving up it acts normal. However if I try to move right or left while in the air the character seems to jitter.

The problem is worse if I change the graphics to "fastest", in that case the character hovers above the ground if I move left or right and just moves down slowly. I get the same errors if I simply run off a ledge (ergo, without jumping).

Also, while I usually don't get the issue in the editor, if I set it to run "fastest" in the editor quality settings, I get the same error in the editor as I did after building it and running "fastest". The issue goes away in the editor if I turn off V sync on "fastest"'s settings, however it still jitters after being built.

I have a hunch that the issue has to do with my recent installation of Unity 5. I hadn't yet built the game before upgrading it to Unity 5, so I can't know for sure, however I've made other platformers using basically the same method in Unity 4 and never had this issue.

Thanks for any help!