Ok guys as usual i need some input on this.I went to englishtown this evening and only ran a 13.6 with a 1.8 60ft @101 MPH.MY problem is that my third gear which happens to be also my strongest and most important gear is locking up on me

I know my car can run 12's but i am not able to do this since i have to slow down and fuss with my third which is being very reluctant to change under high rpm 6900.I am running a ACT 6 puck with rps pressure plate exedy flywheel.Is the mix and match causing this, or am i pushing a little more power than the stock tranny can handle or do my clutch just needs adjusting.
Oh also on this run i hesitated like about a second to get third since it was giving me a pretty hard time to change, which would have drop my time and increase my trap speed.