Why is my build running so slow despite running fine in editor?

Our build is running really slow (like 3 frames per sec) but it runs absolutely fine in the Editor. We're running Unity 2.61 Free. It runs just as slow regardless of the resolution or any of the settings prior to running. Any ideas why this would happen and how we can fix it/diagnose it?

First thing I would check is the output log file (in the same place as the editor log on mac, or in the build's data folder on windows).

If you have problems that only the standalone is experiencing, most likely they'll show up there, and the logging itself will slow you down to a crawl

I know this thread is old but I was having this problem and no exceptions were being logged in the log file. It turned out to be that my graphics card doesn’t natively support DX11 and was probably emulating its API on the CPU. I solved the problem by going to the Player Settings of my standalone build settings, and removing the Direct3D11 API from the Graphics APIs for Windows, and only using the Direct3D9 API.