I think it’s pretty common on an O-320. Ours does the same thing at WOT. I think there’s a John Deakin column that discusses uneven mixture distribution in carburetted engines (and suggests when cruising at high altitude, to back the throttle off slightly, the theory is the change in throttle butterfly position will help with mixture distribution).
Well, it appears to just be a distribution issue related to the throttle butterfly position. Pulling the throttle lever back about half an inch from WOT has little reduction in power but evens out the EGTs nicely:
Regardless of Lycoming recommendations, and depending on CHT, a lot of people sneak back from full throttle enrichment in the climb for this reason, especially given the very high climb rate of an RV.
Once level, you will likely want to be throttled back just slightly (or more), with little effect on MP, to start the leaning process. Then lean it for cruise condition with the mixture lever.
The issue is not of great consequence in terms of fuel consumption on a given point to point flight, although it may be if you were doing circuits. In full throttle climb the carb/manifold is throwing a little extra fuel at the engine for cooling in a fairly haphazard manner.
