Clutch pedal

I did a lot of searching here and couldn't seem to find anything on my issue I'm having.
I recently started noticing that at high rpms (6k+) my clutch pedal gets a lot harder to press down. I've put over 30k miles on my car and never noticed this before until recently so I have no idea what could be causing it. Both transmission and clutch are stock.
The only thing done right before this starting happening was I changed my front caliper/rotors and at one point while starting to bleed them the reservoir got extremely low. Could air have gotten into the lines and be the cause of this?

No, but as a clutch wears it's common for it to display increased pressure on the pedal. I put a new Luk clutch in my last truck and the pedal effort was way too light and as it broke in it started to get heavier