I do know if you keep the gas tank above 1/4, you don’t get the warning

 

Does it really matter if you are out of gas now or 2 minutes from now? You're still out of gas.
The moment that you stop moving with the engine running your MPG changes to 0. When the level is low the sloshing has a larger effect, because of the shape of the tank. If this was last century a "floating needle" might be a thing.

 

The up and down hills, yea, noticed that in other cars.
OK, guys.
I will let him know to keep fuel in it.

Have a good week everyone.
Wayne

 

My last position at GM was in Supplier Quality for Fuel Systems. I was told by several Engineers at GM that this purposely done to limit complaints about the gage going "way down in the first 100 miles". It is designed to be non-linear. They also have electronics called a slosh module to keep the gage from bouncing around as the vehicle gets tilted. It will move eventually, but it's delayed.

It's like those ambient temp readings. They don't always read correctly until you are moving at over 30 mph for 5 minutes or something. All to prevent ridiculous readings from a hot parking lot from freaking people out.