Intel x550t2 slow throughout

[mightyi]

I am hoping someone can help me solve a really frustrating problem!

I am using a Lenovo branded intel x550-t2 card in a custom build pc using an i3-7th gen cpu and ssd.

I have been using a cheapo Realtek based dual 2.5gbps network card and this has been connecting to a 2.5gb switch and the 2.5gb port on my virgin router - both auto negotiate to 2.5gbps and when testing using another windows machine connected to a 2.5gbps nic (intel i219) I get around 1150mbps from my 1gig virgin service.
But when I swap out for the x550, it negotiates to a 10gbps port fine but otherwise only connects at 1gbps. If o force to 2.5, they connect at this speed for the most I can get using the same pc as earlier is 6-700mbps.

I do not have any ids running and only have a basic config on the firewall. I’ve tried the offloading settings but no change.

Can anyone offer any advice how to get this card to negotiate properly and more to the point provide comparable
Speed to the cheap card?

FYI I have just done a completely clean install to confirm it’s not that and it isn’t.