When you achieved the higher number (Verizon states 940/880 in their gigabyte service) did the tech use his device or one of your devices to test?
speeds are dependent on the nic cards installed in your computers. Wifi speeds are not guaranteed at all.
are you using your own router? Verizons router. That also makes a difference since different routers obtain different speeds based on settings and design.
you could call 1-800-VERIZON and have them see if the problem is on your end or on theirs. If they say the speed is fine up to your ONT then it’s a problem on your devices.