guages

my 1993 dodge dakota's fuel gauge dont work, i was told it needs a fuel pump,which comes with the sending unit, not sure about any of it, my ? is that the hot and cold guage flickers up and down, only a little from where it sits above cold. could it have to do with eachother or what? im trying to work on it, and im a complete beginner. also , i want to do a tune up myself and i was looking into the air filter, i saw a breathing filter? anyone know if im suppossed to change that on a tune up? i did get a new box with the speedometer and gauges at the junk yard, could it be only that thats causing my gas gauge to not work and the other to flicker? my speedometer works and my oil pressure guage works.