All the configurations in server.properties and plugins_customization.ini are same when you compare with your old version?
Was there any tuning maintaining at AVOS side?
No differences found between those two files from v8.0 and v8.1 appservers.
Can you elaborate more on the tuning at avos side part?
We had retry mechanism for one workflow in partner link section and that has been migrated too.
Issue appears for all workflows and lag is more if DQ channel execution is present between two tasks.