Upgraded to Gigablast but speeds way below Gigabit

Hello

Looking for some help. I have recently upgraded to Gigablst internet and have been having nothing but problems. Speeds are at best 425. I get that on several computers and a Synology NAS. All are more than capable of getting the speeds I desire. I have had several techs come out and bring their box which reports 1+ gig. That does me no good as I don't browse or download with one of their units, I use a computer. The tech two times before said he would come back in two days with a new modem and laptop to verify speed. He never showed up. Called back to vent and reschedule a new appointment making the same request. A new tech showed up with a modem but no laptop to confirm speeds. Same story as all the others told me. I am concerned because I see multiple posts on this forum with the same problems that are all locked, but none showing any kind of resolution. any help would be appreciated.

Thanks

Dan