That's a great rig. You'll enjoy it. You had a question about the 20" tires. My previous rig had 20" tires and it affected the towing some. The sidewalls on the 20" tires were softer and gave me more side to side wiggle when towing. My current rig has 10 ply heavy duty Michelins, and the side to side wobble went away immediately. The other specs for the two trucks were about the same (engine, design, cab, etc).
The 20" also were listed for slightly lower towing capacity, though you are well within range for your current travel trailer. You'll really enjoy that rig. The transmission you get with the Chevy diesel is one of the very best on the market. It handles towing wonderfully.