Concerning pstack equivalent, have you read Erlang Profiling from official guide? It gives you lot of example on how to profile your application and find where your code stuck.
Another useful tools is observer it will show all working process, CPU usage, process stack and lot of more information.
If you don't see anything with these tools, you can try with Erlang debugger .
Now concerning couchbase, if your application is currently running, you can connect to it with Erlang shell and launch previous quoted commands and applications.
I don't know if you are using couchbase alone or with couchdb, but, if you want to use observer or other tools from command line, you can start couchdb with -i flag:

# -i use the interactive Erlang shell
couchdb -i

In case of your application run remotely without GUI, you can use etop , its a CLI alternative to observer . You can also dump etop output to file if you don't want to run it directly from your Erlang shell. IHMO, if you want more information concerning I/O or debug, use eprof , fprof and other profiling tools with dump file (see also eep profiling tool, easy to use).
Another alternative, if you are using SSH and want to see observer window, you can use X11Forwarding with ssh: ssh -X $yourserver or ssh -Y $yourserver and simply run observer:start(). in your Erlang shell.