People are mistaken when they think there's anything in common between the 1500 and 2500 trucks. Yes, they share the same body, but underneath they are completely different trucks.
Engines, transmissions, driveshafts, axles, brakes, frame, springs, suspension, wheels, steering - all completely different. The 2500 Suburbans are the same platform as the 1500HD pickup trucks.
It's not the engine and the presence of coolers that determines your towing capacity. It's the axles, brakes, frame and suspension. And in that regard, there's nothing similar between 1500 and 2500.