So I don't know if this is the problem because I think you said you swapped out the fuser and get the same results so that is a bit concerning however, FOR SURE try to run short-grain at those weights to help eliminate scratching in general. I was having the same problem on one of my fusers and it came down to the anti-static mylar or tape on the fuser. Took me forever to figure this out and cleaned everything and still would appear. The thing is I DID notice slight burrs but thought nah that's not it until I got feed up with it especially on metallic/foil stock.
I am just suggesting this and its up to you if you want to try it. Here is a picture of where I'm talking. You will notice the anti-static tape on your as oppose to where I removed it. I have not had any problem with this being removed. If you don't feel any "slight" burrs it may not be this but again had the same problem and this fixed it.