fuel gauge problems

My bet would be a bad wiper arm contact on the sender. You might even be able to fix it. You may be aware, repop senders are very inaccurate. There was a thread on here about improving them, and there is a device you can buy called a "metermatch" that is programmable and several different points to correct the reading. I have not used one as such, but I did buy one, set it up and do some testing.