Gearbox Problems Or Is It Something Else?

NISSAN DEALER FITTED A NEW CLUTCH TO MYALMERA BUT TOLD ME THE BEARINGS IN THE GEARBOX WERE NOISY I AM JUST ABOUT TO FIT A SECOND HAND GEAR BOX NOW. HENCE THE CAR HAS NO POWER ON 4TH AND 5TH GEAR AS i DRIVE IT. MAKES SOME SQUEEKY NOISES DOESN'T GO FASTER THAN 60 MPH. COULD IT BE SOMETHING ELSE?
THE CAR HAS ONLY 100K ON THE CLOCK...
ANY IDEAS?
THANKS, REGARDS, MARK.