All calculations are for a stock vehicle and were used for an averige of 21MPG and designed for a desired range. Not everyone with an FJ Cruiser has 285's. I'm averaging 19 on the freeway without the roof rack and coming back from Overland Expo got 25 MPG traveling about 65 MPh. With the roof rack and RTT is about 16 MPG. Friends on fb can see the pics of my scangage when im watching range. My other vehicle has a range of over 2,000 miles averaging 24 MPG.
The replacement tank and reserve are about 72-74 gal depending on how much space is lost due to the charcoal filter and the other little black box under there and will have a total once it's completed.
Here is from Mormon Lake AZ to Vegas 3 weeks ago and includes going up the strip with a Mate. It topped out at 26.2. It was close to ideal conditions, but can get 22 MPG driving from Vegas to LA. I can get close to that going back, but the mileage goes below 18 going up the Baker climb and settles down at about 20 when getting into Vegas. I keep the RTT and roof rack off now and use supreme unleaded (for arguments sake).