Hi, and congrats. I carried a 2017 Hawk on a 2007 Tundra for three years that had leaf spring upgrades from Boise Spring Works. I sold that truck recently because our Hawk was pretty well appointed and we liked to carry extra stuff increasing our weight. I felt we were right at the limits of what we could carry, so I went with a 2500HD truck.
Doing a quick google search, the payload capacity of your 2012 Tundra is 1,575 lbs. Depending on how the Grandby is appointed, you could be over payload capacity. Now, the spring upgrade will help, but you could be at the limits of what the Tundra can carry. You'll find that lots of folks who have a Grandby have a 250/2500 or even a 350/3500 truck.
Setting aside budget concerns, you might have an easier time procuring a new truck than a Hawk shell. The FWC website says 35 - 45 weeks for a 'custom' camper. I'm not sure what Denny at Jackson Hole FWC has in stock. But, if you are happy with the Grandby, finding a more capable truck might be easier than finding a Hawk right now