The problem is probably not the NAND filling up. NAND memory is unlike HDD memory. It does not have 'seek times' like HDD's and therefore do not need to be defragmented. If I had to make a guess as to what the problem is, the most likely would be priiloader (although it is still immensely unlikely to cause a noticeable lag). Try disabling all hacks to see if it makes any difference. Don't forget to re-enable them though!