Row based replication lagging on 5.6.25-73

I did rebuild a slave recntly. the replication is row based. Many MyISAM tables.
Just can’t catch up!

I treid the suggestions on this post, but still can not figure it out

Basically, the IO_thread is the issue, Relay_Master_Log_File seems to be lagging a lot.
The master and slave have same hardware.

Thnak you