The 3.3.5 client is a 32-bit application. HD textures use more RAM. To fix this, most users apply a Large Address Aware (LAA) / 4GB Patch to their WoW.exe to allow the game to use more than 2GB of memory.
Some comprehensive asset bundles go beyond characters to fix muddy ground textures, low-res flora, and blocky buildings. Enhanced skyboxes introduce smooth gradients and high-definition particle systems for weather effects. How to Install HD Models in WoW 3.3.5a wow 3.3.5 hd models
Create a new level 1 character. If the model appears invisible or as a floating cube, the patch is conflicting. Delete the new .MPQ and try a different version. wow 3.3.5 hd models