Question Is my 1080 ti Underperforming?

[aaronfugal]

I play games all on Ultra settings but my FPS for some games I feel like should be higher. Assassins Creed III is only getting getting 40 at 1440p (this game in particular I have capped at 60 but it goes down to 40), the Witcher 3 gets about 90. All my GeForce Drivers are up to date, and I noticed in the task manager that core 0 and 1 are at about 100% usage. Temperatures are not too high. MSI Afterburner says I am using about 60% of my GPU in Assassins Creed III. Also my Nvidia control panel has all the settings maxed out and I have switched to Ultimate Performance in the Windows Power Management. Everything seems to be up to date.

Specs:
Intel Core i7 8700k CPU
MSI GeForce GTX 1080 TI Gaming X Trio GPU
Corsair Vengence 16 GB 3200 MHz DDR4 RAM
Asus ROG STRIX Z-390E Motherboard
600 W PSU
Samsung 500 GB 970 Pro SSD
Seagate 2TB 7200 RPM HDD
H115i Liquid Cooling AIO
4 fans for plenty of airflow
Windows 10 OS
MSI 144 Hz Monitor

 

[aaronfugal]

Someone please answer. Is it my Power Supply?
EDIT: Just got a new 850 W 80+ Gold. Still having the same problem.