Rough running at high rpm after 200hr service

Just completed my fourth 200hr service including replacing all o-rings in my carbs. Engine ran fine for first 45 minutes then started to lose power and run very rough over 4000rpm but fine under 4000rpm. On a full power static runup on the ground it will generate 5300rpm for a few seconds then surge and falter between 4200rpm and 5300rpm. Any ideas what might be wrong? Thanks!