Bit random I know but I've noticed that when I put my remap on the car (using an STS unit) the petrol gauge reads incorrectly. Below us a picture were I've absolutely brimmed the tank then applied the map & the guage has dropped, I'd done 0.3 of a mile since the fill up!
It's weird, I've had to remove the map & reload it a couple of times & was pretty sure the fuel gauge had dropped then, but this is the first time I'd done it with the tank totally brimmed so I knew I couldn't be imagining it.