Poor shifting just in 3 largest cogs

I have a shifting issue on one of my bikes. The issue seems to have arisen after changing to a new chain. I know normally poor shifting is a result of cable or derailleur issues, but I'm struggling to figure this one out. Shifting is great between the 8 smallest cogs (11-21 cogs) both ways. Shifting is really bad specifically when down-shifting (shifting away from the spokes) between the 3 largest cogs (28, 25, 23). Shifting back up towards the spokes is great. The issue is particularly bad if I'm in the big ring, but is still there in the little ring.

Bike is an Orro Terra Gravel. Groupset is full 105 5800 - compact chainset and 11-28 cassette. Chain is a KMC X11-93. I've used this same model of chain on this bike, so I know it can shift very well with the Shimano components.

Initially I thought it was the result of a chain that's too short. 54 links rather than 55. So I added another link back in to the chain this morning but the problem persists.

Here's what else I've done and checked so far:

• Removed cassette, cleaned, re-seated, and confirmed all cogs and the lockring are correctly seated on the freehub.
  
• Replaced rear mech hanger with a brand new one.
  
  

Anyone have any ideas?

Tonight I'm planning to:

1. Swap in another rear wheel that I know shifts well to determine if the issue is on the wheel/cassette.
   
2. If still an issue, replace the gear cable.
   
3. If still an issue, swap in another derailleur that I know shifts well.
   
   

Is there anything else I'm missing, or does anyone have experience fixing this type of issue?