I replaced the 36 gallon tank in our 15 Denali dually with a 60 gallon Titan right after we got the truck over 3 years ago. I found a used, like new on Amazon (which means someone opened the box and returned it) for less than a thousand. Still expensive but I needed the bed of my truck to be open. We have done over 500 miles with it several times which is farther than we usually go. The 60 gallons is more than enough for us. The fuel gauge is spot on but it does mess up the miles to empty. I never tried to see if could be reprogrammed but I don't think it can.
On ours the Titan gets its extra capacity mostly by stretching it both directions. It is a little deeper but is hid by running boards so I never see it.