So i was cleaning up my CC to smooth out my game and decided to try sim PEs guid duplicate checker. it found several pieces of cc, including fixes, that shared GUIDs with the objects.package file and I'm very confused. i was told that duplicate guids would harm/slow the game.
Is this normal for fixes? is it safe to change guids on them? and what affect could this have in game?

It depends.

If the fix is supposed to override a behavior (for instance a recategorizer mod), then it is supposed to use the same GUIDs, or it won't override the original items/behavior.

If it's a new item that's supposed to show up separately in the catalog, then it should have a new GUID. Before you change the GUIDs for anything, be aware that GUIDs are directly tied to the MMATs, so if you change a GUID for a recolorable item, you also have to change the MMATs for all the recolors to match the GUID. Sometimes the original item has already been fixed, so you can redownload if you know where you got it.

It's a good idea to check if the object really needs a new GUID before you set about fixing it. All "conflicts" may not be something that needs fixing.

If it shares a GUID because it has an override of the OBJD, that's not a duplicate. It's only a duplicate if it has a new OBJD with (usually) group 0xFFFFFFFF that has the same GUID.