Getting slow downs in combat? Instances causing you fps problems when they never used to?

Yes, it's badly written mods which are causing the problem, and here is one that will show you which are the offending articles:

(Those that haven't used a MinnaMod before, you may want to drag the cute doggy button to your minimap and then type "/minnabutton lock" to prevent it from moving)

WARNING! When profiling is Enabled (always requires a reloadui, don't panic you get a warning when it is about to do this) things ARE much slower than normal, this is because the scripting system profiler is turned on.

The best way to identify a problematic mod is to turn it on for a trash pull, and watch the percentages which are updated every 5 seconds. Then turn it off once you've found the culprit.