your synchro is worn. it causes your gears not to line up properly for shifting. hense the grinding noise. there is no magic cure in a bottle. youll need to have the tranny serviced. ive seen a few with this problem. ford will warranty it. they did mine and actually installed a new unit as it was less expensive for them than rebuilding the original unit. for the few thousand it cost for a tranny it would be worth talking to them about it.