Feul Gauge is lying to me

My 97 jimmy 4x4 & 02 sonoma 4x4 fuel gages have a mind of their own. When the tanks are full is the only time they tell the truth. Otherwise the gages fluctuate. One example: the 02 sonma, periodically it will be at a 1/4 tank. When I put the truck in reverse, the gage will go to empty. when I put the truck in drive, the gage goes to 1/8. I'm pretty sure this is a crimped wire, but I don't know where to look. Does any body know what I'm talking about?

Good Ground?

Good Ground?
Where do I look?

Rear cylinder head and left rear on frame crossmember.
Which one are you going to start with?
Always check dash gauge for proper operation.
For good ground.
Run a voltage drop on the ground wires.
On fuel tank sender ground check for good ground at wires going to tank I would catch the ground wires going to fuel tank and Jumper a extra ground wire to them.

It's a well known problem on the '97.

I had to replace the sender unit on the pump on mine.
(there's a thread up in the "How-to" section, complete with sender p/n.

Ended up dropping it again for a whole new pump assembly,
and again a thrid time when the Carter pump crapped out 14 months later.

Don't use Carter, or Airtex.
Use Delphi/ACDelco.