97 GT speedometer

I've been reading through some of the posts about console problems, gages dying, lights coming on, and although I have a similar problem, I think it's different enough to post about. So here goes:

97 GT, 72k, no mods. Every once in a GREAT while, usually after I accelerate pretty hard, the speedometer gets "stuck" at a certain speed, then, if it decides to move at all, jumps around and eventually up to the actual speed. When I slow to a stop, it seems to work fine (i.e. after I'm below 35 or 40 or so, it just drops off naturally). I can get the speedometer to work if I give the dashboard above the instrument panel a quick, but sharp swipe with a fist, and that seems to get the speedometer back in working order.

It's been doing this now for about 8 months, and like I said, usually happens when I accelerate pretty hard, but more often that not, it's working fine. Does this seem like the whole instrument panel will need to be replaced, or could it be that the needle is messed up somehow? If I need the panel replaced, how much do you think a dealer would go after me for? $500?

Any thoughts would be great!

Thanks.