Using a pressure cooker

I never really mastered my Fagor pressure cooker because it is a bear to get unsealed. But, was in a hurry to make pot roast so thought I'd give it a try.

The meat was a very nice boneless chuck, which didn't really get all that tender. So, question #1, would another cut of meat get tender? Or is low-and-slow the only way to go?

Question #2 - I thoroughly oiled the gasket, but it still was almost impossible to open, even after it was completely cooled down, until I used a screwdriver to jiggle the gasket loose. Suggestions?

I must say -- I used a couple of cans of beef broth, and enough chopped onion, potato and carrot to fill the pot halfway, and various herbs, and the broth and veggies were very, very nice, so I was encouraged by that. The meat had a nice flavor but was not tender.