I like to start at a simple point that any properly equipped 1/2 ton pickup can pull any Airstream. Then get into the details.
Any particular model pickup's towing specs often range from under 5000 to over 10,000 lbs. The chassis and brakes are shared between the models' variations. What makes the difference in towing capacity are primarily tires, overall gear ratios and motor size. Tires and axle gear ratios can be changed to upgrade a used truck, should you buy used. So can transmission coolers.
The biggest variable is what is hanging on to the steering wheel.
I pull a 6000lb+ Airstream with an older, small motor 1/2 ton and with a newer 3/4 ton. The 1/2 ton has upgraded tires and gears, and has done an admirable job for years. The 3/4 ton does it easier, but the huge
difference between the two is not their towing or weight capacities. It is the sophisticated digital engine and tranny controller integration system on the newer truck. My driving style varies between the two, but both make for safe rigs.
Towing my 10,000 lb cargo trailer is where I see the biggest difference in the trucks' capabilities. The 3/4 ton handles it well with any cargo load distribution and even without WD/sway bars. The 1/2 ton is used to pull the cargo trailer only for lighter loads with the WD/sway system attached.
I say buy a truck you like and go from there. If you plan lot of mountain travel, a bigger motor is nice.