What is this on my floor pan?

[SilverMiner]

I'm tearing out the interior of my 1980 K10 Silverado Suburban. Once I got the carpet and vinyl backed jute out I was surprised to learn I still wasn't down to metal floor pan. Instead I found what you see in the attached photo. The photo is looking at the drivers side floor pan with the front curve of the door seal visible in the lower left.

The floor appears to be covered entirely with this moderately stiff vinyl material. Based upon the primer found underneath and the body color on top, it appears to have been glued on at the factory. I've owned quite a few of these rigs and have never encountered this vinyl floor covering before, but this is my first 1980 model.

I plan to remove all of it even though it seems to be an important part of GM's sound deadening scheme. It seems to be stretched over the top of some low spots in the pan and I'm concerned it can trap water and promote rust.

After finding this, I'm wondering now how much improvement I'll see installing the my new sound deadening material versus what GM provided.