Like Bluto, ours is a Curt Magnum V. Bought one year ago for our Silverado 2500HD 4x4. Fit was nearly perfect, I had only to rebend exhaust pipe one inch for clearance behind curbside rear wheel. Difference between oem and this Curt is ridiculous, especially considering GM had the oem receiver rated as class IV-V.
The Curt weighs double the oem receiver. The Curt is very soundly constructed, based upon a 4X4 steel box channel crossmember and a pair of thick and very deep flanges on the sides. The Curt mounts with four 1/2" bolts into the chassis plus two into the bumper, the oem only has two on much shorter flanges under the chassis plus the two under the bumper. The Curt seems to handle well the torsion from the weight distributing bars, the oem rotated and failed to help keep the truck's front end from lifting when loading the hitch.
I'm relieved to get the oem receiver off before outright failure. A friend, also with Chevy 2500 and towing a 31 Classic, experienced a catastrophic separation of receiver tube from crossmember on his oem receiver.
Sometimes spec grade is just not what you want to depend upon, unless it is mil-spec.
regards, Jim http://dreamstreamr.com