What games and framerates exactly? What resolution? The 7870 is a very respectable card for gaming at 1920x1080/1200.
Did you re-install your drivers?
1920x1200 i play on i am currently playing world of Warcraft . medium/low settings 60+ fps
It just feels not worth the money i paid to put this rig together.
CPU= i7-3770k 3.8ghz
MB= intel dz77ga70k
Ram= corsair vengeance 1 stick of 8gbs
GPU= Radeon Hd 7870 2gb
HardD= 1TB hard drive western digital 7200RPM
OS= windows 7