Well first of all, that's not an 84 Centurion Prestige. They were only made in 85, 86 and 89. It's not an 85 or 86 either. It could be an 89 with a repaint. That being said, if you haven't done it already, I'd make sure the headset is adjusted/working properly. Also try it with a couple of different wheelsets to see if that changes anything. If it needs a fork swap, Tange made/makes a chrome fork out of Prestige tubing. You could get one of those.

Here's what the various years of Centurion Prestiges looked like.

Centurion Prestige