Wrath of the Lich King is a veeeeeeeeeery old expansion and it runs on almost deprecated graphics APIs.
First of all, do the Large Address Aware on the wow.exe as suggested above. Second, make sure you have DirectPlay enabled( search
turn windows features in the start menu). Run
this to make sure you're not missing any of those old DirectX components(WotLK is, after all, using DirectX 9).
The rest is spray&pray and hope windows 10 doesn't randomly decide to do its own sh*t in the background, hogging cpu cycles. Remember, it's an old game on new hardware/software - contrary to popular belief, it can't run perfectly.
Also, put the "wod models" client to rest. It's problematic. Just use the original 3.3.5 client with its original models.