Been driving my car and up till today it was working and shifting just fine. So today when i was driving my car wouldn't shift as easy as normal. I had clutch pedal pressed all the way in and when i went to shift its like it wouldnt go into gear so in order to shift i basically had to slam stick up or down to get it in whatever gear i was going into.. when car is turned off the shifter moves around and goes into 1st 2nd and 3rd just fine but when car is on and running its really hard to get it into gear. i am wondering if this could be air in the line or slave cylinder or something else.