Chevy & GMC Vans

Last year while driving on vacation my gas gauge needle started wobbling around like it was in a paint mixer. This happened for a few weeks until finally it settled down to just being inaccurate, not reflecting the actual amount of gas in the tank. (I keep track of usage with the trip meter and always filling the tank.) Now it drifts around slowly as I drive, from Full to 1/2 tank, all on its own.

I have had the gauge cluster tested and replaced, the pump/sender tested and replaced, the Powertrain Control Module tested and replaced, grounds checked, and general wiring checked for breaks/kinks/intermittents. Still the same.

My mechanic, who has kept this 1998 Astro of mine running like the day it was new (now with 148,000 miles) cannot figure out what is wrong. I have let him tear into the truck for what has amounted to weeks of time cumulative, to no avail. He even took it to a Chevy dealer, on his dime, to see what they had to say. They couldn't figure it out either.

Any help out there?

Many of us have seen the needle vibrating like mad but the needle going from low to high and back and forth is fairly rare. With all you have replaced, I don't know what it could be.