You can switch to 2 tablets, but at some point you'll have to take a break from the pre-workout caffiene altogether. Every time you kick up the dosage your body will eventually get used to it and it won't work any more. That's why you see these teenagers who drink 5 monsters a day like it's nothing.
If you take a few weeks off the stimulants you'll find that you're far more sensative to them when you start using them again.
Current PRs at 242- 495, 335, 565, 1395