With 900 pounds of people in the Burb, you run out of payload (~1500 pounds) quickly. 600 pounds of loaded TW means about a 4500 pounds loaded TT, or 3500 pounds dry!
I would upgrade the Burb first. If you can find a similar vintage 03-06 3/4 ton, especially with the 8.1L, you can tow nearly any TT you find.
$20k for a 2007 Rockwood Signature is way too high. Those go for $20-25k new, at least in the mid west. 2014's have been in production for at least 4 months, so it is 8 years old!
So, with your $20k budget I would:
Sell Burb, get more capable one for about $2k-5k.
Find any used TT you like, probably cheaper driving it home from the mid-west.
FWIW, My TT was $18.5k + TTL/WDH brand new. There are less expensive models. Check new pricing from the "wholesale RV dealers" in the mid-west to determine if new and/or the drive it worth it compared to local prices.
