Sounds like you didn't set your shield up with an appropriate ArmorAddon record. The art settings in the Armor records are only for the _GND (dropped) versions, what your character actually wears is set up in the ArmorAddon records.
All you would need to do is duplicate the DragonPlateShieldAA Record, change the Biped models and First Person models for Male and Female to point to your own mesh (the same mesh you used for your _GND model can be used), then in the table beneath the World Models for your shield's Armor record, set it to point to your ArmorAddon instead of the default.
Also, in the future, retexturing objects can be done completely inside the Creation Kit now. Just give your new texture a TextureSet record, then duplicate the default ArmorDragonPlateShield record, open the Edit Model window for it, and in the table where you can specify alternate textures, point each of the listed entries to your TextureSets. No need to redo the model unless you need to change the UV Mapping.