My viewhands nor starting pistol will change in game when I build my mod.
I've changed the viewhands and starting pistol many times before and triple checked to make sure I did it correctly.
For some reason it seems as if _loadout.gsc doesn't count when I build my mod, even though it's checked.

Check your appdata mods folder and look to see if updated loadout is in the iwd.

I don't see it
Should I check mymapname.iwd and edit with Notepad++?

In your appdata mods/mapname folder there should be mapname.iwd
It has the folders that you see in the mod builder tab in launcher. The loadout just gets moved from the directory launcher is using to the appdata folder when you build the mod.

If your using harrys perks i think it has a loadout in the iwd and you would need to edit that loadout.

Editing files in the appdata isn't a good idea because it will get overwritten when you compile.