I just went down and moved a pile of bumpers around,,,,,Lots of them had GM stamped on them. A couple had GMU. The one ton bumpers had GM, along with something else i couldnt make out.
I have a Ting-Tang china repro bumper on the back of my suburban.
Also have a orig GM bumper on the rear of my panel.
When both are parked side by side,, you can definitely tell the difference. Like having balsa wood in one hand and a 2x4 in the other.