fuel gauge on colorado/dmax

Hi all,
I just bought a second hand dmax with 86000 kms on the clock in almost new condition. I have put around 1000 kms on it and noticed it had very bad fuel economy. After a bit of investigating I noticed that my fuel gauge is not reading correctly. In short when I have only a quarter of a tank I can only get 39 litres in a 76 litre tank. Another example when it's almost empty it's should take say at least 65 litres but it only takes 46 litres. So in short the gauge is miss reading by a quarter of a tank.
For those of you with colorado/dmax's has anyone experienced this issue?

Is there a fix.

Cheers.

Not sure if it's still under warranty but needs a scan and re calibrate
Dealer or can be done through the right auto elect.....
Sounds like it still has some warranty have a look if your service book is dealer stamped up to date and have a read through the warranty booklet
Dealers will always charge you for something :/ Warranty or not

I have a Dmax,2015 model. Sometimes with 1/4 of a tank,if I park on a hill nose down the gauge shows dead empty with the empty light flashing until I fill it up again or somtimes if I drive onto level ground and turn it off and then back on it comes good.I haven't had it at a dealer as an indy does my servicing but maybe I should get it checked out.