Clutch slipping... dealer says this.... Please help.

To make this short, the SRT-4 my friend bought had some tranny problem, I went to were he was and listen to it and it was chatering from the bell house. Well come to find out it was something withthe flywheel. The place he bought it from said it was basicly held on by two bolts. Well they replace the clutch and flywheel, Now my friend is telling me when it seems to hit 5 psi but It is when it is warm and it is hitting 14-16 psi it slips. Could this be the Huydralic cylinder or somthing different? The mitsu dealer is telling him it could be this. Could he have had engine problems or is there somthing we can check? Could they have put in an SXT clutch or could it be motor problems?