So I'm having trouble with my Ultegra RD cable tension adjustments. If I adjust my tension so everything works well,,quiet and smooth in 1-5 by the time I get to six on down it needs help. If I then make barrel adjustments to smooth out the bottom end it doesn't work back on top again.

While working my way from 1 down the cassett towards ten I need to loosen the cable to smooth out to add some travel. If I make it right I need to then tighten back up on the opposite side working towards 1 again.
I just replaced the RD because the old one did the same.

It now seems something else is going on and I can't fix it.

Any tips for a newish mechanic wanting to learn to work on my own bike???

Thanks