Ram GVW Question

[metro36]

I have been considering upgrading from my GMC 2500 w/6.0 to a diesel, to handle my larger trailers better. I found a good deal on a 2012 Ram 2500 with the Cummins. The only thing holding me back is the GVW and payload. The Dodge has a 5500lb front, 6000lb rear, the gvw is 9000 and it is rated to haul 2100lbs. Now a GMC diesel 2500 has a 5200lb front, 6200lb rear, the gvw is 9900 and the payload is 3100lbs.

My question is, what is the reason behind the ram only having a 9000lb gvw? My current 2500 has a 9500lb gvw and the payload is 3500lb. Its very rare that I will be hauling over 2100lbs in the bed but I like to have the capacity. I have a 200 gallon skid sprayer which would take up the payload when full (I usually only fill it to 100 gallons but I might need it full in the future). Can someone explain why ram made the gvw what they did? It seems to me like the truck could be a 9500 or 9900lb truck.