Lagg issues

I would concider my pc above avarage or atleast not complete horse****. Run wow in Ulta with 2560x1440 (Wide) 24-bit color and 24-bit depth 2x multisamble Windows Mode (Maximized) and i lagg like never before.... Im am no computer pro but i sould say i should be able to run wotlk with all max settings with no problems?

I tryed to remove Windowed Mode and go Fullscreen and then the game is completely lagg-free, which is great. I dont like fullscreen, i alt-tab alot and there for i use Windowed Mode. What is wrong and can i do something go make Windowed Mode as smooth as fullsreen?

GTX 1070, i7-77 @ 3.6Ghzm 16GB RAM and some M.2 SSD. I have a Asus 2560 x 1440, 144Hz G-Syng monitor. Asus VG-series 3D ready (Both 27").

I use the following addons:
ACB
Action Bar Saver 2
Aesa 0.9.5
Afflicted3
AzCastBar
Bartender4
EventAlert
GearScore
Ghost: Pulse
Gladiminish
Gladius
Key Bindings Profile
LoseControl
OmniCC
Preform AV Enabler
SnowfallKeyPress
SoundAlerter
TidyPlates with Clean Plates cusom plates
X-Perl


TL;DR I lagg af when i run the game in Windowed Mode but in Fullscreen it is all ok. Can i make Windowed Mode to not lagg?