Scratching my head here. After a Nvme m2 ssd upgrade I am not getting the full Link width of the Pcie bus which should be 4x, as I understand. System profiler reports back as only 2x. Blackmagic speed tests show read/write of 700-750 mb/s, which confirms the link width of 2x. The mac is the last of the great 11 inch MBA's , fully specced, i7, 8gb ram and (up until now 500gb ssd disc). I have upgraded the original Oem Apple Samsung 500gb ssd to a 1tb Adata sx8200 pro with an Sintech m2 adapter. The latest version of Mojave (10.14) is running. I restored from a time machine backup, on a separate hard drive, after booting from a Usb stick. The previous ssd reported via system report a Link width of 4x and this was born out with read speeds of over 1400 mb/s. I have reset the Pram, the Smc, and even tried another Samsung 970 evo blade; that also reports back as only a 2x link width. Any ideas as to what I can try next?