Are you using 50/50 antifreeze/water or Evans water less coolant? There is around 25F difference between them in coolant temps.



Do you have all cylinder's exhausts monitored for egt ?



Carbs out of sync can cause different egt readings on different cylinders .



High egts can mean inefficient burn in the heads. Proper plugs? gapped at what?



Prop pitch can affect heating, over pitched and you will generate heat. lugging the engine will do this also.



Did you try increasing rpms ? to 5300- 5500, sometimes this will make the engine run cooler.