having problems shifting my truck, can it be anything besides the clutch going.

My standard 5 speed Ford Ranger is getting very hard to shift. The clutch is
not slipping, smoking, or smelling, but the shift doesn't want to go into the
gears. If I drive very smoothly keeping the RPM's down it shifts better,
sometime even great. The exception is first gear. If I come up to a red light
and shift when slowing down, it is OK sometimes, but from a full stop it can
be very hard to get back into first from neutral. My mechanic put a new
master cylinder in, but it had not made much difference. I assume it is the
clutch, but this is the first time i ever saw a clutch go out just from not being
able to shift, and like I said sometimes occasionally it shift like its old self, but
then gets difficult pretty quick. Can there be any other reason besides the
clutch?