my guess is the fuel sender is bad. in the tank.
did you check the resistance first?
low ohms say 25 full or over 100 empty
and NEVER infinity:?
if it measures wrong , at the harness,
then its bad. or its conn, rusty.
so you must drop the tank on most cars to do this.
all this is covered in the FSM.
or all covered at alldata.com, log in read. (fuel system chapter)
ill answer for USA car, no engine options stated, (that too can change answers)
SUB 1500 , not 2500 answer. not stated that either.
4.3L ( of the 5 engines,)
ill quote the FSM (alldata page)
remove tank (sure drain it first.) the sender on this car is with pump assy.
1 Remove the fuel tank. Refer to Fuel Tank Replacement
Remove the fuel sender assembly retaining ring using the J 44402 (Image 1)
2 Remove the fuel sender assembly and the seal. Discard the seal.
Important: The fuel strainer must be in a horizontal position when the fuel sender is installed in the tank. When installing the fuel sender assembly, assure that the fuel strainer does not block full travel of the float arm.
see special tool to remove the assembly , clamp ring from tank.
buy the FSM
or login to alldata.com and read the instructions, warnings and all steps.
its non trivial.
but dont do it of the resistances read good.
first do the tests for the sender
and only replace it , if really bad.
why do all that work for 1min test..???/? <<< seen 10,000 times this forum. all guessing, sad to see.