You need to change your mental view of your ability. By saying you can't go any faster, you will not be able to go any faster. As soon as you start saying "I can go faster", you will be able to open yourself up to new possibilities!
Do I sound enough like Dr Phil?
Hahaha...
On a more helpful note... if you're playing as much as you are, and not getting faster, try something different. Doing the same thing over and over will likely lead to the same results... so maybe try a bunch of different setups, try focusing on using all the track, try being extra smooth, try only lifting slightly in places where you lift right out of the throttle, try just lifting in places where you currently brake. The beauty of a sim is that you can try absolutely anything you like with no repercussions. So experiment!