Actually it seems (and it is logic) that the Unity engine is faster as standalone than in the editor (of course when you don't have to run all the editor around, and i dont even speak about the profiler...) so knowing that :
Physics will be able to happen more often and it will make more precise calculations, so small details which are not spotted in Editor will be in the build version like small tile differences, and also forces may be applied more accurately and/or more often which could prevent slopes limits to work proerly...
That's not all though you should take a look at your project properties, in player and check if you are running the Editor in Standalone mode and if your selected quality setting is the same.