Our butcher sold us Denver steaks instead. Any adjustments to the recipe needed? They were expensive, so...

From what I've read, Denver steaks are from the chuck, flat side of the shoulder. They are relatively tender with good marbling. Here's some great info on them: http://www.foodrepublic.com/2016/04/06/beef-talk-what-is-a-denver-cut/

I think it's going to be similar to short ribs, in terms of the fat marbling, but I would not cook as long as the recipe instructs, maybe shorten that cooking time of 55 minutes in the pressure cooker. to about 35-40 minutes and see if it's ok. I always fear overcooking meat. If it's not tender enough you can always cook it some more.