i did look at the manual i was quoting, and was guessing that he had the 16 gallon tank on it and not the bigger one, for obvious reasons

 

Chrysler depends on fuel in the bottom of the gas tank helping to cool the submerged electric fuel pump and motor. This is especially important in hot weather. To insure that these parts get cooled they leave a large 4-8 gallon amount of fuel below the E mark on nearly all their vehicles.

You can custom 'trim' the resistance of the fuel sender to change this.
see info below:
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When full the tank sender should read 20 ohms plus/minus 6 ohms.

When empty the tank sender should read 220 ohms plus/minus 6 ohms

If you get corrosion on the electrical plugs the tank sender will read more
than 26 ohms when full and your needle on the fuel gauge won't go as much past
'Full' as when the vehicle was new.

 

I had just changed my "cai (really wai)" back to the stock box and i went from getting 15.2 mpg to getting about 18 to 19, especially cruising at 80-100 mph on the highway for a good 80 mile trip. so my gas mileage definatly went up. I called my dodge dealer and they said that it has a 16 gallon tank and that they do leave about 4 to 5 gallons past the empty mark to keep the fuel pump running cool. just fyi

 

I have an '01 4x4 with the 4.7 L engine. I recently drove it on a 600 mile round trip and it got 18 mpg highway. I was running it at 70 - 75 mph pretty much the whole way. In the city, I get around 13 mpg.