Profiling Vim

To find which plugins may be causing certain actions in vim run slowly try using the built in profiler:

:profile start profile.log
:profile func *
:profile file *

Then perform the slow action, when done run:

:profile pause
:q

You can then open the profile.log file and look at the bottom to see summary, sorted by run time, of which functions took the most time, the function name may give away which plugin/core function is causing the issue. The top of the file will contain each line of code that was run in vim during the profiling session and how long it took.