What have I done wrong?

[46 the goat]

Hi Everyone, I am using an Akasa Venom on an i3. Couple of questions please, I have replaced the TIM that I originally used ( supplied with the cooler ) for Arctic freezer 5 and my temperatures are several degrees higher than with the original. I have downloaded the instructions from Arctic for fitting to an i3 and have followed them to the letter, I have tried twice with the same results. I am tightening the fixing nuts so that the cooler feels firm on the CPU without any movement, should I tighten them more? how tight should they be .
I am going to try one more time today when I get home from work, so any ideas will be appreciated.
Thanks
46 fan