sendust

Hi guys this is a little lengthy but i want to make sure all info is included. About a year ago i had an issue with the dash lights being dim, tested switch not the issue, i eventually removed the entire display and cleaned all contacts with emery paper , this brought back the shiny copper look. After i reinstalled the display the lights worked perfectly, dimmer switch worked as it should, after a short while i noticed my heat gauge never came up over 1/8 and my fuel gauge would move about a 1/4 of a tank reading while sitting still. I did a short out test and gauge went to full, i cleaned the area the the ground strap connects at tank, this seemed to improve some. When filling the tank the gauge went to over full and seemed to work but it seemed to drop down while driving much quicker than before, when the gauge showed empty i found the tank still had about 7 gallons in it. I decided to replace the sending unit and now my gauge goes to almost 3/4 when full and still fluctuates between 3/4 and 5/8 when standing still. Do you think this is a faulty gauge, if so i have a spare ( any way to test before installing) or could it be the small unit that plugs into the rear of the dash i think it regulates power ? any thought appreciated Pete