Clutch Cables?

I recently replaced the clutch on my car, drove for 4-5 months with no problems. Now I am losing 2nd, 4th, and reverse from time to time while driving. If I jiggle the shifter, I can get things back in order and get into the needed gear. Do I need to replace the clutch cables, or is there something else I can check first?

I would bleed the slave cylinder at the clutch. It may not be fully releasing the clutch to shift fully into gear, hence it will not stay in gear. Also, the shifter may need to be adjusted.