Backstory - 85 4Runner, SR5 gauge swap done 5 years ago

Recently my fuel gauge started to bounce around unless the tank was completely full. I've checked the connections on the instrument panel and pulled the sending unit twice. The first time I pulled it I cleaned it out - the second time I bent the metal that touches the variable resistor in the sender to give it better contact.

The problem is still with me. Searches here and on POR show people's gauges working to a point and then dropping to empty. Mine isn't doing that so I'm thinking I still have a bad ground somewhere. I did find a couple people with the same problem as me but they didn't follow up on what they did to fix it.

I'm trying to avoid buying a new sending unit unless I know that is what's wrong. The sending unit checked out per the FSM, by the way - that's the other reason I don't want to replace it.

Any suggestions on other things to check?