I don't think Chima Nwachukwu's speed speaks to anything. I don't think he had speed and lost it.
As I posted, he is credited with a 4.48 40 before the draft. That would have been after his senior year. Like I said, he wasn't a blazer, but I don't recall his speed being a total liability either (his 40 time would support that).
Why'd he get caught by a lineman? If I had to guess, he, along with the rest of the defense was probably gassed having to chase around Hawaii's WRs all game. Wouldn't surprise me if he was a little banged up as well.
John Estes, the Hawaii center credited with the tackle ran a 5.34 40. So, I can tell you with certainty, he was not capable of chasing down Chima in a straight up foot race, without some kind of extenuating circumstances.