My Archer A8 router is significantly slower over both wired and wireless connections than wired straight into the modem.

i have 1 gig connection and when i connect wired directly modem my speed is around 1.1 gig

when i switch and connect with router max speed  i got is 880mbps.

also when using wireless i never get over 600mbps

I've scoured the forums for a solution and have tried updating the firmware, turning on/off Qos, NAT boost, and alg settings, factory reset.

contact with spectrum support and then they sent a technician but nothing change.

Nothing seems to work.

Any help for that ? or just insufficient model ?