David- I've got the same problem, although the gauge on my car reads about 1/4 tank too low. The problem was there when I bought the car 2ndhand at a dealer with 3 month warranty, so they took out the sender, put it back in, checked the tank ventilation system, put it back in, checked all the wiring, drained the tank, checked the amount of fuel going in, checked the sender again and so on and on. Ultimately they concluded it was the gauge itself. So you may well have the same problem. Unfortunately it's part of the whole instrument cluster, not easy to replace, and probably very expensive. I've learned to live with it and use the day trip meter to keep an eye on the distance driven after a fill-up.
By the way, unless I'm very much mistaken you can get at the sender by taking out the rear seats (not the backrests). There should be a hole there through which you can get at the sender.
'95 2.0TS 16V