Until Hidden Path gets a chance to fix this issue (which they are well aware of) the following steps may help you.
I’m running Windows 7 Ultimate x64 bit, and have a PC beyond the optimal spec’s for Age of Empires 2 HD released on Steam this past weekend.
After initially installing it and loading it up, I noticed lots of FPS and lag in multi player and single player games.
I disabled multiple monitor support in Windows, and found that the lag and FPS dropped immensely.
How to disable multiple monitors
I have two monitors plugged into my PC right now. To disable the other and enable only one monitor:
Right click the desktop, go to Screen resolution.
See the screenshot below and ensure that in the Multiple displays section you’ve selected ‘Show desktop only on X’ (where X is the monitor you want to use in full screen).
After taking these steps the game is very playable for me, and quite enjoyable.
Thanks to Hidden Path for remaking this gem.