My gauge reads full when it really is at half. When I fill it, it pegs the gauge.. Think this is the sending unit in the tank or a gauge issue?? Any help would be appreciated

 If you can disconnet the wire at the tank, with the key on, the gauge will go to Full. If you GROUND the signal wire, the gauge should go to Empty.
It seems like your gauge will at least MOVE some, correct? That means the wiring is ok. Your problem is going to either be the float is hanging up on the bladder inside the tank, or the sender unit is faulty.

I'll add that it could be a problem with the gauge itself, but the sender unit has caused more issues like this than the gauge.

|UPDATED|1/24/2014 10:48:16 AM (AZT)|/UPDATED|

Thanks for the advice. Now all I need to do is get under the car.. If I need to change the float or sending unit, I'll assume the tank needs to get dropped. With it having a bladder in it, should I look at changing out the entire setup?? The car is garaged and no obvious rust etc on the tank, but it is 34 years old..

I believe the sender unit can be accessed from the TOP on your '80 car. Remove the fuel filler door, and the rubber boot inside, and you'll be able to check the wiring, and pull the sender out of needed. Others here have done that, and may be able to give some time saving tips.