I'm looking for a non-core mod that can extend the slider length and extend the amount of sliders you're able to have. I currently have the one from here, but I also want to download error trap as i am playing on a save file that has existed for 5 generations of sims and its size is causing a lot of in-game problems.

Master Controllers base mod will allow you to extend sliders. You will need to edit your sims through the NRaas menus, because it won't affect your sims when entered through CAS or Create a Household.

People at Nraas might be more capable of answering this, but I don't think that Error Trap and Cmar's Xcas core mods are incompatible, per se? Yes, they are both core mods, but they don't modify the same script files, to my knowledge?

But yes, Nraas MasterController's solution is also good.
Just something more, if you have MasterController and its Integration module, you will get MasterController's functionalities in the regular Create-A-Sim from Edit Town, Mirrors, Dressers and Styling Stations.

And then there are those of us weirdos who use ErrorTrap, MasterController, XCAS, and another core mod or two thrown in for good measure all at the same time. It's okay to run multiple TS3 core mods as long as they don't impact the same game core resources in conflicting ways. Managing MC and XCAS together can be a little tricky, I've found that the increased number of sliders as specified in MC must match the value in XCAS' accompanying tuning file or else unexpected things can happen (well, not so unexpected, otherwise the additional sliders might just stop working).

The MasterController Expanded Tattoo module, however, is incompatible with the full version of XCAS and is not needed.

Probably more info than the OP needed, but maybe of some use?

Nah, I actually like having a lot of information just for reassurance lol, thank you to everyone who responded!