Stress testing New MacBook Pro RAM Modules

I have a mid 2009 MBP. I recently got an 8 GB upgrade kit and installed it. I then went to memtest86.com and downloaded their Linux bootable ISO and started testing my RAM. After a few hours, I started running into errors, I then reseated the RAM and faced the same issues. So just out of curiosity, I put back my Apple RAM and ran the test again. I started getting errors on that too.

Now, I am not really sure whether there is an issue with the Apple RAM. I had dropped it off at the Mac store a few weeks back and they replaced a bunch of things and I would assume that they would have caught any serious issues then.

Can someone clarify whether its even possible that I am getting false positives on memtest? If so, are there other tools that I can use? ( I checked up memtest86+. The forums there had some mention of people having issues with Intel Macs. So I am not really sure what counts as a reliable way to test Intel Mac RAMS)