04 Aztek Gas Guage
 

My friends wife has an 04 Aztek.
The gas guage randomly jumps, and will then peg on full.

I'm thinking that it's a loose ground, or something physically wrong with the sender. I'm not very GM familiar, so I'm looking for some basic info on the GM sending unit and gauge.

Where does the sending unit ground to, or is it just one wire to the gauge and it grounds through the tank?
Are there any known problem prone connectors that cause this in the dash?
I assume that the dash is all electric, so pulling the cluster there won't be a speedo cable correct?

Thanks for any input on this one, I'm a Jeep guy, so real good with wrenches and random electrical problems, just completely unfamiliar with the newer GM stuff.