Kernel panics are almost always hardware related. Once in awhile they come from poorly written software, but you were right to replace the RAM. Apple is also pretty good about helping you diagnose these problems. If you are convenient to an Apple Store, make an appointment with a genius and they'll put it through its paces to see what's causing the problem. Another tool I'd strongly suggest for your arsenal is Tech Tools. A copy comes with AppleCare or you can buy the Pro version. (If you already have AppleCare but lost the CD, you can download it here by entering the serial number of your machine: https://support.apple.com/techtooldeluxe...)
I agree with Gabe's explanation. The best place to purchase your upgraded memory is from macsales.com. In my experience, they have the right memory for your Mac. I owned the same model and tried to upgrade it with a chip from Kingston which brought my laptop to it's knees. The chip tested good, but my MBP would only work when it was removed. When I returned it and bought the chip from macsales, everything worked.