It could be too many plugins, as I was having simiar problems. Just get the New Vegas Plugin Utility from the Nexus, and then merge the plugins that you think woud be alright together. I would ignore any quest mods as this will reset them (think of it as installing the mod fresh), weapon mods will be the same, but I would still merge those together. I have about 5 different .ESPs containing about 10-20 mods each, and with no issue, but I still have about 60 other plugins that aren't merged. You could merge all of these together: Anoher group of mods you could merge: You would just have to disable the original .ESPs as this won't remove them, it will just copy and merge those copies together.