As far as content goes, it depends and changes from time to time, but to give you an idea of how small the difference between top 3 and top 10 like you're seeing is, it could be a word (yes one word), a phrase of two words, a couple of plurals instead of singulars or singulars instead of plurals.
It could be the order of the words in a paragraph or two. The difference in the positions you're talking about is small, tiny, almost unnoticeable.
I remember talking to someone here (or reading it here) who added one word to a page and it went from position 43 to the top 10 results. That's how small the differences in rankings are even a bit lower than the differences you're talking about seeing, so you're not off by much anywhere and it's definitely not Panda if what you're saying is the difference you're seeing in positions.
My advice is to look at the little things and see how you can improve those to be a bit more targeted for your terms (removing some words as Leosghost suggested might be exactly what you need to be more focused and concise about your topics).
Also don't expect anything to happen overnight or get frustrated when it doesn't. Things don't usually change that fast (in the up direction anyway) too often these days, so part of it's a change and wait thing.