Bro, try out this USD$0.99 app called Free Memory. It doesn't requires any jailbreaking and is available publicly over at App Store. Just use the search tool and look for Free Memory. You'll be shocked to see that the average remaining RAM around 3-4MB! Thats why everything is so slow. Click the free memory button and it'll free up to 20MB of RAM sufficient for most programs. Give it a try.