Egad! Why are you adjusting the limit stop with the cable attached? The high limit screw sets the reference for the whole system and needs to be set without cable tension. So start the adjustment process from the beginning. Shift into high gear, remove cable tension, set the high stop (align pulley with 1st cog), attach cable, take out the slack, shift a few times to make sure the slack is out of the cable but only adjust in the small cog, shift into low gear, set low stop, fine tune.
Other things to check:
1. Derailleur hanger alignment
2. Cables and housing dirty, frayed, etc
3. Dirt/debris jammed in your derailleur