could be the clutch cable and this is how you check:
adjust biting point significantly further away, ie, you need to
release clutch lever further to hit biting point. if at this new
biting point your gear problem solved, then confirmed its your
cable. if u comfortable wif this biting point, keep it this way,
else change coz your cable worn out. however, it could also be that
all the while your biting point is much too near and just need
adjusting rather than worn out. if not, than its worn out. cable
cost bout $14.