2005 Dodge Srt-4 Clutch or Clutch master cylider malfuntio

For the past week I've been able to shift up through the gears without a problem, but when downshifting it has been nearly impossible to get into 2nd or 1st gears. Now, however, it will only ocasionally go into gear. When it does it's usualy with a thunk. It will start while in gear but will not come out of gear. I hear no grinding, however, the clutch pedal vibrates under foot. In order to get he car home I had to turn it off at any redlight in order to put it into gear. Sometimes though it alowed me to shift while still moveing but only with more than average pressure.