This answer is going to sound silly, but I see it with my students all the time.

Are you sure that you are depressing the clutch pedal to the floor and that the carpet is not obstructing the path?
It doesn't take much to make it look like a clutch or synchro problem.
Lazy shifting is often the culprit. Pay attention to your high rev shifts, and let me know.
Sometimes, with the seat pulled back to far, your leg doesn't extend enough, and you don't realize this because high rev shifts are done too quick.

If all is O.K., AJ is right on with his diagnosis.