Screen resolution messed up when upgrading to latest Macbook Air

I have a macbook air 13' from 2013.

I just bought the same model, only newer.

I backup up everything on an external hard drive via time machine on the old mac, then used migration assistant to copy files and configuration to the new mac.

Of course both machines were updated to the latest Yosemite 10.10.3, as Apple suggested.

Things seemed to work smoothly, with a correct copy of everything.

Alas, no. I have an external monitor, which is perfectly recognized on the old mac, correct model and resolution:

But on the new mac, same exact model, just a tiny difference (Intel HD Graphics 6000 1536 MB, instead of Intel HD Graphics 5000 1536 MB), the screen is not recognized at all and the resolution is all messed up.

Been on this for hours.

• I tried SwitchResX, didn't help.
• I tried using both the official Apple VGA adapter and a third-party. Same results.
• I tried pressing the

  alt

  key while choosing

  scaled

  on the display preference pane to force 1920x1080, it works, but the x-axis is all stretched smaller and moved about 400px to the right.
• I tried changing the res via command line, didn't help.
• I tried looking for mac drivers for BenqT220HDA, they don't seem to exist as a separate file.
• I tried flashing the NVRAM etc. Multiple times. Didn't help.

Ideas?