I'd honestly check the ground in the trunk first, probably the more accessible item. Also more likely to be at fault if the resistance directly at the sender reads normally.

Might also have to check the IVR output. Thats normally done with a test light or an analog meter since it pulses on/off. If its not pulsing reliably the gauge reading will go funky. I think that one you have to pull the cluster to access.

not sure on the other connector. There are several down in that area, and accessibility is questionable at best. Lots of crap packed into that space.