If you're still running the factory installed OS, consider rooting and installing Ubuntdroid. When I got mine out of the box, it was slow and I wasn't sure I wanted to keep it. I decided to root it and now it runs very fast- I'm not noticing any lag at all. Ubuntdroid works on both Sprint and VM versions of the phone. Just be aware that rooting the phone voids the warranty unless and until you re-flash with a stock rom - unrooting the phone.
