Assuming 48" water depth, your pool is close to 21K gallons, right?
According to this chart, you are about where you need to be for filter size.
[attachment=0:qd2jht2p]FilterSize.jpg[/attachment:qd2jht2p]
However, there are some doubts about this. Remember, these are minimums. Many of the experts here will recommend going almost twice what this chart shows.
But, lets get back to your original problem. Clearing a cloudy pool. You seem to be on the right track, keeping your FC level appropriate for the SLAM process. Your pool will clear with the filter you have, it just takes time, and several cleanings of the filter. Yes, I know it can be a pain in the backside, but if you continue to follow the SLAM process and clean your filter when your pressure rises 20-25% above clean, you will get there.