Last night I had gone on a S3 mod installing binge, re-organizing my mod folders and carefully downloading and installing my chosen mods from MTS:
Long story short, this is the kind of thing I spent an all-nighter learning how to avoid and it happened anyways: When I got in the game, the camera in ET and Live Mode was extremely slow in moving and rotating. I simply cannot play like that with my anxiety and have spent the last 2 hours looking up ways to fix this issue... and nothing.

What I've tried:

1. Editing the VideoCamera.ini folder
2. Clearing my game cache files
3. Taking out many of the mods
4. Looking for help videos/old posts
5. Reloading the game several times (takes forever)

My last resort is to come here to bug you guys. Thank you for reading this and help is greatly appreciated.

Agree with most of the above, although I would probably be most suspicious of the Camera Mods category first. Then all the rest.

That last sentence though, I'm sorry but TS3 can have more than one Core Mod as long as they don't conflict by trying to control the same core resources. There are only five Core Mods meant for current patch levels and in popular usage, so the number of such conflicts is pretty small and this issue usually becomes more theoretical than practical.

NRaas ErrorTrap - doesn't conflict with other Core Mods
NRaas UntranslatedKey - the same, but it's really for developers and there is only a 1.67 version currently; most players should not need this
AwesomeMod - can work with NRaas with some steps taken to reduce duplication of features, not a problem with ErrorTrap
CmarNYC's XCAS (full versions) - does conflict with AwesomeMod and these two should not be used together, it's fine with the others
Consort's 2X Weight/Fitness - not sure if this is meant to work with Awesome, is fine with the others

That's all there is really unless something new has just popped up very recently or unless players have designed their own Core Mods. The other bazillion mods out there are Script and Tuning Mods, and scripted objects. Conflicting Script Mods are indeed a source of pain but it's much more challenging to figure out which ones do conflict and shouldn't be used together. Most offten that just comes down to trial and error, and by not adding them all in at once as nitromon says.

If I understand this description correctly, there is now a sixth core mod?

Asymmetrical Relationships by lizcandor

Not that this is relevant here since it doesn't conflict with most others but just to have a complete list in case someone googles and ends up here?

Hmm, thanks for pointing that one out. There was also a sixth one the list around a couple of years ago courtesy of Gamefreak130 (World Loading Screen Overhaul), but thankfully he redid that one as a Script Mod as the conflicts were otherwise more than a bit much to manage.

Asym Relationships seems very new though and apparently for some it's kicking up core version warnings on startup -- that's a sign that it isn't yet properly accounting for the internal build numbers of the different current patch levels and install types. There appear to be some other issues on that one that are still being worked out, but I think I can see why it may need to remain as a Core Mod as there probably isn't any other way to have accomplished what its developer set out to do.

So yes, maybe it does belong on the list of now six. And in the meantime, if the OP has that one in play it should probably be set aside for now until everything else they require is running in a more stable manner.

Lied might be a little strong and it might depend on if we were on a very early patch when something contradictory was stated.

I was a bit later coming to the game than many here, so it's possible that multiple Core Mods were an issue with the original release. Or folks just assumed so, since I think this was a thing with TS2, maybe?