I wrote a post on the whole cluster work & resistors to tweak the fuel level reading (search). Re sender tweaks, it is simple & obvious. Bend the tabs back on the cover to expose the resistor & wiper arm. Bend the wiper arm outward so it contacts tighter. The arm is stainless so should hold that tension for a long time. Of course use a multimeter to measure the output resistance signal as you sweep the arm (free w/ coupon at HF).