Got a weird one here and need some help...noticed today that my fuel gauge does what it wants...left work with a hair less than half tank drove maybe 40 miles the next thing I know it's dead on E with the check gauges light on...back story is its a 99 xl 3.0 flex fuel 5 speed n it does have codes for rich on both banks which I knew gas milage would suck because of it but the weird part is I pulled into the closes gas station and gave her 5 gallons got back in and turned the key and bingo went from dead on E to just above half and also noticed the gas gauge chances with the hills going uphill shows more gas down hill shows less...now I just put a brand new fuel pump hanger assembly in 3 days ago because of chasing the rich codes but the gas gauge was doing all this since I bought the truck...if anyone can make any sense of this it would be much appreciated

 

More than likely the Anti-slosh module is going bad, its on the back of instrument cluster, a separate circuit board
It there so the gas gauge does NOT go up and down when you go around corners and up and down hills
It samples the float level every few seconds to average it out so no sudden movements

Most common failure mode is gauge stays on Empty or Full all the time

Google: ford ranger anti-slosh module

You can use jumper wires on the module to by-pass it if you can't find a working replacement

When you have the instrument cluster out test the Yellow/White striped wire on pin 12 of connector C215 with OHM meter(see diagram)
1989 and up Fords use these OHM readings
Empty = 16 ohms
Full = 160 ohms

So hook up ohm meter to yellow wire and ground wire, should see a stable ohm reading between 16 and 160
Rock the truck to get gas in the tank to slosh around, moving the float up and down
Should see ohms changing as that happens, smoothly, no jumping around
If its jumping around then the sender in the tank is the issue