How Can I Find Transaction Replication Information

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SQL-Server-2008R2

Like an alert created that tracks replication subscription application processing time (how long it tables the actual queries that insert/update records). I want to know the duration if it last longer than 15 seconds and I want to know if those long running spids are blocking anything else during that time (number of blocked spids)

I know the regular blocking alert does some of this work, but I want to focus specifically on replication SPIDs. Right now this is primarly just information collection to focus performance tuning efforts, which may eventually morph into an alert. Ultimately, we want to avoid replication blocking taking down.

Also would like to know as we have lot of blocking issues and most of the times it was due to replication so how can we identity replication blocking processes and along with Distributor:Subscriber Latency(I have below script to check Latency either on Publisher to Distributor or Dist: to Subscriber.
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SELECT SUM(cntr_value)/1000/60 as ReplicationLatencyInMinutes FROM sys.dm_os_performance_counters (nolock)
WHERE counter_name in ('Dist:Delivery Latency','Logreader:Delivery Latency');