Gauntlet IV - button presses don't register consistently

[BlastBrothers]

This is an odd one. Any inputs (even in the menu) are extremely sluggish and buggy. It's like the game only successfully reads the controller 10% of the time. The success rate seems to vary depending on CPU load - you can at least move between menu options, but once the game starts you're functionally immobile.

[BlastBrothers]

Problem has changed in 1.0 - inputs are fine but the entire game runs about half as fast as it's supposed to.