Fuel Gauge and Air Pump Question

I have a 2001 Jimmy 4x4 with the 4.3 in it. When i put it in park the fuel gauge moves back and forth and wont stay steady. Heres an example when in drive it says i have 2 notches below 1/2 tank i shift into park it moves 1 notch past 1/2 then goes 1 below 1/2 and moves back and forth between 1/2 and the notch below it. I havent noticed it before any ideals on what could be causing it?

Also i m on my third air pump in my jimmy and on this last one i had it redone so the hose is rerouted away from the fan, but my ses light came on giving the air pump code. I can here the pump running and still feel it getting air. What else could be wrong causing the light to come on?