Ok, quick update and a bit of info for all other guys out there who may have the same problem. After much messing around and the problem getting worse, I went over everything again. Turns out the new caliper was faulty, one of the pistons was stuck/sticking, the other had a small leak on it. Note to self, sometimes even though it is more expensive, it's better to pay the extra cash for Lexus genuine parts! Problem solved :0)