From these symptoms, either the guage is off (high resistance) or the voltage limiter is not right (low output). But I am assuming that the guage and limiter operation were the same in '76 as in earlier years. The sender resistance range seems about normal, at lesat for all earlier years; some quick checks indicate that the Aspens used the same resistance range so the system look to be the same for the '76 as for the older cars..
Have you changed the voltage regulator to the solid state, and is that a 7805 voltage regulator? Do you have access to a 5V power supply? The best way to troubleshoot that will clear this up is to feed the gauge and sender with a known good steady 5v and see what you get.
Does the temp gauge seem to read right when operating and driving the car? If so, then that is an indirect indicaiton that the limiter is OK, and all that is left is the fuel gauge itself being off. These are thermally activated gauge movements; there is a heating wire coiled around a bi-metallic strip that bends when it gets hotter (fuller tank). Its movement is mechanically connected to the needle. It might be the heating wire, the strip or the needle. See here:
http://www.nls.net/mp/volks/htm/fuel_ga.htm