As expected, once I got the truck on the road I'm finding issues to fix. In this case, it has to do with an inaccurate fuel gauge.
I filled both tanks, gauge reads full. Drive around for a few days, front tank reads empty. Switch to rear tank, gauge shows full. A few more days, gauge reads empty and front tank still reads empty.
Fill rear tank and it only takes six gallons. Same with the front tank.
I'm thinking the sending units are not working right, but odd that both would be off by the same amount. Is there a way to test them without dropping the tanks? Can they be replaced without dropping the tank?
The sending units have a high failure rate on these trucks. The way they are made they wear out prematurely. I suspect both are bad.
If you want to run a test, take the wiring plug loose to the sending unit, find the sending unit wire(usually yellow blue or blue/yellow) and with the engine off'key in run, ground this wire at the sending unit and then unground it. The gauge should read full scale back and forth when you do this. If it does, the guage/wiring and switch are good, the sending unit is bad.
You can get to the front one barely. The rear tank will have to be dropped or the bed taken off.