I understand the problem with the slow fall, try activating it when the character is already falling. If you activate it during the jump, it won't work (I'll make an adjustment after the jam so that it activates at least at the end of the jump before the fall to avoid problems).
I'm glad you liked the game (the T key function was a test that I ended up forgetting to remove when uploading the game to the game jam, hahah).