I'm not sure what could be causing this issue. When I export my LWJGL program to an executable .jar my FPS gets destroyed. I've tried providing more RAM to the JVM, but that didn't help.
Interesting, never experienced such an issue. Can you provide more details? Did you profile your application?
I used VisualVM and compared the IDE application and the exported one. Both were showing very similar results. I'm honestly not sure what info to give you.
Are you using VSync and is any other application using also VSync in the background?