System slow-down - disk usage?

I'm on v5r4, and we've recently gotten a very large customer and have had some speed issues. At first we thought they were specific to some certain new programs, but today we discovered the issue was impacting another job that was completely an absolutely isolated as far as programs go. So, we were looking at things from a system point of view to see what changed to cause this other job to slow down so much. Our guess - that our % system ASP used went from ~60% to ~70%. Is it possible that that would cause us an issue? (We had a job that would normally run 5 hours take almost 24 hours.)

We IPL'd over the weekend as well. Anyway, I realize this email is probably lacking a lot of specific information, but I'm not really a systems guy, and we're kind of grasping at straws, so I thought I'd see if such a change to disk % used should have such a big impact?

I am looking into other performance improving methods, but at this time we'd really like to pin down the cause of our performance crawl before attempting to put in enhancements.

While I'm at it, I'm curious how to quantify "excessive paging." I've seen reference to that phrase online, yet can't seem to find a number.

Thanks,

Kurt Anderson
Sr. Programmer/Analyst
CustomCall Data Systems