I was reading this and noticed it seems like you are all 1999 and 2000 models.
There has been an factory updated circuit plate for the instrument cluster and calibration procedure released to remedy these issues on these specific years.
I'll update this with pictures and part numbers soon but wanted to get this to you guys before you dove into anything.
ELECTRICAL
EL010-00
Title:
FUEL GAUGE INACCURACY
Models:
'99 - '00 4Runner
August 4, 2000
Introduction
Some owners of 1999 and 2000 model year 4Runner vehicles may complain of fuel gauge operation problems. These complaints may include:
^ The gauge reading will gradually change while driving or will show a different reading after cycling the ignition key "OFF" and then "ON".
^ The gauge will come off of "FULL" quickly.
^ The perception that the fuel tank capacity is less than it should be, or differs from the capacity stated in sales literature.
To improve these concerns, a new Circuit Plate No. 3, fuel sender gauge and suction tube assemblies have been developed.
Applicable Vehicles
^ 1999 - 2000 model year 4Runner vehicles built between the VINs listed in this bulletin.
IMPORTANT NOTE:
^ Some 1999 vehicles have had the updated Circuit Plate No. 3 installed during production. Please see the Affected VIN Ranges section.
^ Refer to the specified Repair Procedure in the Affected VIN Ranges before ordering ANY parts.
Warranty Information
Applicable Warranty*:
This repair is covered under the Toyota Basic Warranty. This warranty is in effect for 36 months or 36,000 miles, whichever occurs first, from the vehicle's in-service date.
* Warranty application is limited to correction of a problem based upon a customer's specific complaint.
Parts Information
*IMPORTANT NOTE:
Replacement of the No. 3 Circuit Plate will cause the odometer to be reset to zero. These parts must be ordered directly from the vendor. To order a part with the original vehicle mileage restored, please reference P.A.N.T. Bulletin 00-01.
Affected VIN Ranges
Please refer to the illustrated VIN ranges to determine the appropriate action.
Repair Procedure
1. Replace Combination Plate No. 3.
A. Verify that the replacement circuit board has been ordered with the correct vehicle mileage for that vehicle. See important note.
B. Remove the combination meter assembly.
C. Remove Circuit Board No. 3.
D. Replace the circuit board with the new part.
E. Reassemble the combination meter assembly.
F. Remove the fuel tank.
NOTE:
When removing a tank that is not empty, verify that the tank is secured to the support device, to prevent fuel spillage.
2. Replace Fuel Sender and Suction Tube Assemblies.
A. Remove the suction tube and fuel sender assembly.
B. Remove the fuel pump assembly.
NOTE:
This part will be reused.
C. Install the new fuel sender onto the new suction tube assembly. Align the hole of the fuel sender mounting bracket with the fuel pump bracket hole. Make sure that the bracket of the new fuel sender is butted up to the bottom of the original sender mounting bracket. Tighten the 5 mm screw.
Torque: 1.8 - 2.2 Nm.
D. Reinstall the old fuel pump into the new bracket assembly.
E. Feed the wire harness between the fuel pump bracket and the fuel pipe, and connect the white connector.
F. Install the new assembly into the tank.
G. Perform the Fuel Gauge Calibration Procedure (See TSB EL010-99, dated December 24, 1999).
H. Verify correct gauge operation.
