GM gives your 2500 trucks a 6200 rawr that will carry all the load in the bed. The new 2500 GM rear axle can weigh in the 3000 lb range leaving around 3200 lb payload in the bed. Load the truck up and weigh front and rear axles separately. That way you will know how much in the bed payload you have available.
This is one big reason we see mostly 3/4 ton trucks safely pulling good size rv and non rv trailers out here on the roads. Same truck as the 3500 SRW GM exception can be a rear overload aux spring pack.