The gauge may be stuck because it's gone south, or it may be reading high because there is residual pressure keeping the needle reading at 55 lbs.
What I would do is remove the oil line from the back of the gauge, and see if the needle returns to zero. If it does, you probably just got spritzed with some oil. /bcforum/images/%%GRAEMLIN_URL%%/sick.gif In that case, I would remove the oil line from the gauge to down by the oil filter and blow it out with some compressed air, because it somehow got plugged up and retained pressure. Remember, I said REMOVE the oil line FROM THE CAR. You don't need dirty oil sprayed all over you new leather interior.
The last alternative...If the needle remained high after removing the oil line from the back, is that the mechanism and needle itself is somehow binding up inside the gauge. I had this problem with my TR3 years ago. The pressure gauge would go to 60-65 lbs during running, but would then drop to about 30 psi when I shut the engine off. I just took the gauge out, took it apart, put it back together, and it worked fine. Apparently the needle was somehow interfering with the gauge face, and never dropped to zero.
The oil gauge in a TR3 is a simple mechanical device that isn't prone to failure. If something is bad inside, you will see it if you take it apart. It will be some little lever or whatever that broke.