The answer is simple – the problem lies with your computer, not with Heroes or the HD mod. These symptoms occur when the computer slows down due to the antivirus running, or due to a virus, or due to a large number of open programs, or due to a hardware malfunction... The game doesn't slow down noticeably even on a second Pentium if the computer isn't overloaded. Therefore, look for problems in your computer.

My question was not understood correctly. The game itself doesn't lag for me. Unpleasant sensations occur in two cases: 1) When playing in windowed mode. My hero moves, but if I move the mouse at the same time, i.e., move the cursor across the screen, his turn slows down. 2) In full-screen mode. Also, during the hero's movement, the movement itself is slowed down (here I mean that I'm not even touching the mouse; the movement is slowed down on its own). I repeat, all other actions do not cause such problems.