Any idea of how I can troubleshoot why the execution of stored procedures to perform transactional replication is slow, sometimes the duration is 0 and sometime 2100 so quite big variation in duration time?
It is possible to write all replication activity to a text file, but it can get rather large very quickly for the most detailed logging - http://wp.me/p3Vxvi-bx
This might help to provide some insight to the behaviour, or at least help to narrow down where you should be looking.