At 7 miles on the odometer I had the 52 gallon titan tank installed as I could not see how a 31 gallon tank would work towing our TT in the wide open spaces of Oregon, Nevada, Utah, etc. where we do all our camping. 3,000+ miles now and so far so good. Works like this as others have suggested: When filled the gauge sits at full for a couple hundred miles. Then it goes down as it normally would with the OEM tank. I don't know about the distance to empty as I have never used that feature. I do know that the truck correctly calculates mpg though.
I had it installed at Cutting Edge Customs in Post Falls, Idaho. There was only one thing I had to have them adjust after they completed installation. When empty, the tank cleared all underbody parts fine. Once filled, it expanded a bit and was touching the rear fuel filter. They thought it would be fine, but I was concerned about vibration wearing the plastic especially on washboard roads. I also did not want any issues when I have to have the fuel filter changed. So I had them loosen the fuel filter bolts and there was enough play to move the fuel filter over about 1/4 - 1/2" so there is no longer contact when the tank is full. I have not had my first oil/fuel filter change done yet so I don't know if the dealer will complain about the tight clearance. Looking at the design of the fuel filter I don't see that only having less than 1/2 inch of clearance to the tank will be any issue at all. I hope I am right.
I would talk to Titan about your specific truck. If you have the crew cab short bed like mine it will be tight, but will fit. If you have the long bed, it should be even easier to install. One thing different about the Titan tank is that it does not have a heat shield on the side like the OEM tank does. On my truck, the installers did not think that mattered as there is lots of distance from the exhaust system to the side of the tank. The drive shaft is even in between the two. Once, after a regen when the EGT 3 sensor had shown temps over 1,000 degrees, I stopped the truck and crawled underneath to check this out. The fuel tank was ambient like to the touch. It did not appear that the high temps of the regen had any impact at all on the tank. Not sure why there is a heat shield on the OEM tank other than maybe the same tank is used on different models of truck and other trucks have less distance between the exhaust and the tank side.
I have a 3500 so did not have to think about payload. But since you have a 2500, you may want to consider how another 21 gallons, (approx. 150 lbs.) of diesel will impact payload. Probably not enough to be a concern though.
By the way.. The installer and Titan told me that on the new Rams there was no way to use a program to update the tank size. I don't know if that is correct as it works fine for me as is, just like
@jeffn described.