I am also experiencing these issues and would very much like some assistance.
I have been suffering from NPC and player load lag. This can last up to over a minute before the NPC, perhaps with a quest, will load and I can interact with it. Also, enemies spawned for quests. On more than one occasion I have summoned an enemy for a quest only to have it beat on my while invisible and untargetable because it hasn't fully loaded.
Additionally I have been suffering from issues with the music being out of sync and or just straight up cutting out.
And finally, every once in a while the game just crashes, giving me a C++ run time error R6025. I haven't noticed anything in particular that has caused this as it has happened mid-fight, during a teleport, and also just running through Ul'dah.
I am using a wireless connection for the time being, and my comp specs are as follows, in case this has anything to do with it (though, from what the above poster is saying it sounds like no):
System
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Manufacturer System manufacturer
Model P5Q DELUXE
Total amount of system memory 8.00 GB RAM
System type 64-bit operating system
Number of processor cores 2
Storage
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Total size of hard disk(s) 932 GB
Disk partition (C

812 GB Free (932 GB Total)
Media drive (D

CD/DVD
Graphics
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Display adapter type NVIDIA GeForce GTX 650
Total available graphics memory 4096 MB
Dedicated graphics memory 1024 MB
Dedicated system memory 0 MB
Shared system memory 3072 MB
Display adapter driver version 9.18.13.2049
Primary monitor resolution 1280x1024
DirectX version DirectX 10
Network
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Network Adapter TP-LINK 300Mbps Wireless N Adapter
Network Adapter Marvell Yukon 88E8056 PCI-E Gigabit Ethernet Controller