Just got mine done today. They did indeed get a complete new gas tank. The service guy actually called back to the tech and checked, and the tech was like; "Yeah, this box is HUGE!"
It took from 9AM to 3PM (6 hours) to do the work.
Unfortunately, when I picked it up, as I started the engine it was running REALLY rough! I figured maybe there was some air in the line so I revved it and I could smell unburnt gasoline! So I went back in, told the service guy and he sent the tech out. The tech took one look at my engine shaking back and forth under the hood and he agreed something was very wrong. He limped it back into the bay and after about 15 minutes checking, they called me out:
Apparently when they refilled my tank from the "Gas Jenny" with the fuel they had pumped out of it, they didn't realize there had been some old some fuel leftover in the Jenny from a previous use, and it was fouled! Of course, this fouled the fuel they pumped out of my jeep, so I ended up with half a tank of bad, fouled gasoline in my nice shiny new gastank!
They made it right though. They gave me a free loaner so I could go home, and then spent the next two hours draining the tank, flushing and pumping drygas through all the fuel lines and the engine, filling it with 5 gallons of fresh gas and then driving it down the the gas station and gassing me up to full (I had started with a 1/2 tank) just as an apology for me having to go through the trouble. So yeah, they made a mistake, but no damage done, and they did exactly the right thing in making it right.
As for myself, I took "Libby" out to the car wash and got her all cleaned up and polished nice and shiny to go with her new gastank, then took her out on a rarely patrolled section of local highway and "stretched her legs" to make sure she was running good. She was! (Zoom!)