Thanks for the comments...
It's a 2000 model. And runs fine, but the guy I got it from said he had had to put a new transmission in it, so I know its been worked on. And it doesn't seem to "gun it" when you punch the accelerator - it gets up to speed - but on its own time.
For example, I had a heavily weighted 5020 JD with loader on my triple axle trailer and left it at the farm the other day. We had a small shower so the trailer sunk slightly (an inch or so)into the soil, but it was on a rocky hill that was pretty flat on top. When I hooked back up to it, after the rain I couldn't get the trailer moving without loading up a handy man jack on the rear pushing it forward and even then, it just barely started moving and pulled on out.
Mine has the "overdrive" button, too, in the end of the gear shift, but it seems to not work anymore since the light doesn't turn on or off now.