2000 Ford Expedition Running Rough before Gas is empty

Hello,

I have a 2000 Ford Expedition that I recently purchased and it seems to go dead when the tank is a quarter of a quarter tank. When the dash is telling me I have 40+ miles to go before empty. When I stop at a stop sign or a stop light and press on the gas, it doesnt go at first which causes me to press harder and then it like jerks out. It runs fine but it jerks every time I stop and press the gas to accelerate. I've let the gas light come on and the car said I had 20 mile to go but it literally gave out on me in the middle of the street it got up to about 30 miles and then when I pushed on the gas nothing, it was just pressing to the ground with no acceleration. When turned off it would start back up again but then go in and out of giving gas and not givivng gas. The mechanic told me to put some gas and I did and it has been running fine. But my issue is even with a quarter of a quarter tank it should still be working fine without stuttering. Basically I wanna know if this is normal should it be stuttering when the dash is telling me I can go 40 miles and it's still aways away from the red/empty sign. Is this caused by a bigger issue than just not having enough gas. Also i'm only getting about 10 miles a gallon is there a way to increase that?