When compared to the phenom he was pre-prison, post-prison Tyson suffered from: 1) Lack of combination punching 2) Predictable, tamed head-movement 3) Questionable Stamina Personally, I believe most of these things were attributable to poor training habits and the overt lack of a consistent dedication to being the best heavyweight in the world that he possessed before prison. I think his decline was less about a deterioration in skills/reflexes and more about his work ethic/motivation (or lack there of).
I think his skills/reflexes were done for by 2000 by the Golata fight. Everything prior to that was just purely down to a poor work ethic. After 2000 it was all because of being truly shot i.e. finished from a skills/reflexes point of view and ofcourse the same poor work ethic.