I have Premiere Pro CS6 installed on a 2011 iMac (2.5GHz quad-core i5, 4GB RAM, AMD Radeon HD 6750M w/512MB). I know it's not the best computer out there, but I would think it can run this program. However, I have issues with the video preview. The audio will play with no lag at all, but the video generally shows only 1 frame every 20-30 seconds of playback. Obviously, this makes the program largely unusable. Are there any settings I can adjust to make the playback function smoothly?