Please help with tranny/clutch/shifter problem...

I have about 350 miles on my car and I have a problem.....Here is the situation....When the car is running i can't put the car into gear because it is either too hard or just grinds. When the car is off it shifts great. The tranny is freshly rebuilt, new clutch, new pressure plate, new throwout bearing, and new shifter. I am thinking that the arm that holds the throwout bearing is shot because it is the only thing that is not new....I want to get the parts then just do the unstall in one day. I am thinking the tranny is comming out isn't it?

Eric