Also check the vacuum link I posted on page 1.. Seems a lot have that issue around 50,000 onwards k's.. It's something you can check yourself in 30 seconds..
Although it happened after the DP install, it's possible it's nothing to do with the DP's (or surrounds) themselves, but more the fact that you're just running more boost..
I had two issues when upgrading to COBB and DP's:
First was a coil and plug replacement, and then two months later, it was a vacuum leak, which was fixed with a $5 hose.