could be heaps of things,more info is essential,
so u changed the clutch, are there any noises you now hear that were not there previously?
Where is the power lost?
Have you got a boost guage in there? if so what does it read - was this the same as previously,
What computer are you running, vacuum lines didnt get knocked off at all....
give as much info as u can dude, otherwise no one will be albe to help you.