Soldato
That's odd, are you sure it's set to 144hz in the monitor properties in windows? Go to Display Settings -> Advanced display settings -> Display adapter properties -> Monitor -> Screen refresh rate
It's okay, I was being stupid. I was using overwatch to test and had the res set in game to 2,560 x 1,440 (90). I missed this because the frame rate was going above 90 regularly. Doh. Set it correctly and it's all working fine now.