Changed the log reader agent profile to PollingInterval = 1 and ReadBatchSize = 5000.

Restarted log reader agent.

But seems that does not help.

Delivery rate is still always 1.

From replication monitor, the "Last action" of log reader agent shows something like "Delivering replicated transactions, xact count: 3888, command count: 4401".

The message remains there for about half minute, then the numbers (xact count, command count) changed a bit. This behavior continues.