When truck is in motion going down the road gauge is all over from empty to full when stoped it reads properly

The values differ in all types of cars. Older cars peg out at 90 ohms. Newer cars range between 0 and about 400 ohms. Dis-connect the connector at the sender. Ground the sender wire and the gage should read empty. un ground and it should read full. They use a ceramic resistor in the tank that usually go bad.

it's just either the gas gauge is being faulty

the float that is the sender unit in the tank is stuck this is why the gage jumps to full

when the tank is full the resistance is low so the power through the gage make is read full
as the tank empties , the resistance increases so the less current means the gauge reads less until empty there is little or no power , the gauge reads empty
simple check , turn the ignition off, no power , no gauge reading

I have the same vehicle and my car actually was full of gas, registered empty & left me on the side of the road..It was the sensor in the fuel line that had to be replaced.

very well sounds like the sending unit in the tank. Try running some octane booster and fuel injection cleaner in tank of the truck to loosen any deposits on the float.

According to what I read, test the gauge first. Hook power to where the white wire attaches. Hook a ground to the black wire connector. The gauge should rise to full. (May take a while). When on full, the tan wire connector to same ground. It should go to empty. If both work, gauge is good. To test sender, in the empty position, your ohm meter should read 0-2. 1/2 tank should read about 40, and full should read 84-88 ohms.

sending unit on fuel pump is bad, the sending unit shorts out gauge will go to empty or full, never read right, turn on switch ,it goes to full or empty, ,check the pump,hope this helps,thanks robert b.

Fuel level sending units are known to go bad on these.

Mostly likely you have a tank mounted fuel gauge. If your vehicle is pointing down hill the guage goes up or down. It is usually the fuel level in the tank that makes the float go up to tell you how full the tank is, if fuel is sloshing around then level fluctuates. I would say that if it stabilizes on level ground and at a stop, and you can get a stable fuel reading then this is more of an annoyance than a problem. If you can get an accurate reading and you do not run out of fuel you may want to leave this one alone, you will have to drop the fuel tank and replace the fuel float on top of the gas tank which can be labor intensive as well as expensive.