The way I determined what was out of synch was by using the Validate Subscription option

If you open Replication Monitor > click on the Subscription Watch List Tab > double click on the relevant subscription > select Validate Subscription from the Action menu, and then the next time the replication job takes place the system will validate the replicated tables on the Publisher / Subscriber (see attachment)

It will then list out for you any tables that are not in synch

You have two options when selecting Validate Subscription:

As a basic row count (so this is fairly quick)

Check the data within the rows (never done this, but expect it to take a lot longer)

That at least gives you an idea of the scope of the problem, if you don't already know

As mentioned in the other thread though, I don't know of any way of having the tablediff utility go through and check all tables within the replication model

When I had a problem with un-synched tables, I had only about 6 tables out of synch so it was no biggie to run tablediff 6 times

If you have hundreds of tables out of synch, then you may have bigger issues than what tablediff is designed for