For some reason, the 2012 and a few years before MegaCabs had absurdly low payload capacities. I don't buy the argument that the cab weight is the difference as the crew cab is almost as big and if you have an 8' bed with the crew cab, you're still similar in dry weights. I almost feel like they have to have different springs or suspension or something to justify the lowness. Maybe they assume that the MegaCabs are going to be people movers and not towing. But I don't know.
If you look at the Ram Body Builder guide
, you'll see that they aren't right at the 10,000 GVWR so I don't think it's the whole commercial truck/do not exceed 10k registration thing.
In model year 2013, the MegaCab numbers are back up like they should be. My only issue now is that I really like having a 8' bed and you can't get that with the MegaCab. If Ram every introduced their long hauler truck like they prototyped, I'm betting it would be a niche hit. It was a MegaCab, 8' bed, oversize fuel tank, auxiliary tank, air suspension and I think even had air ride seats. Would be expensive, but a sweet freaking truck.