87 300D Fuel Gauge Gremlins

[Tpawlik]

I just stumbled onto the great article that Jeremy 5848 wrote a couple of years ago. My needle is not jumping around. When I fill the tank the gauge reads full. After about 350 miles the gauge reads 3/4. When the needle reaches the 3/4 mark the needle plummets to empty and the reserve light comes on. I removed the sender and left the wires connected. When I tilt the sender to make the float move up and down in the tube. I can make the gauge read empty and the light comes on, but when I tip it the other way the gauge still reads 3/4 instead of full.
Has anyone had this problem? I am going to take the unit apart and see what it looks like in there.
Thanks to Jeremy for the great info.