Replication Monitor reports little to no latency, but my tracer token is taking hours to go from Distributor to Subscriber
For my money, tracer tokens are a really good way to monitor latency. I don't know what the latency metric in replication monitor is measuring, but I've personally found it to be unreliable. For my environment, I post a tracer token through a SQL Agent job and then monitor the token's progress by looking at the token tables in the distribution database.