Screen Scraping and hoging system resources

Hi Group,
We are running two of the largest's i series box's that IBM released
(installed early 2000.,)
They are soley used to run interactive green screen Rumba sessions
(maybe 3000 per day)
and I have 20 to 30 Screen Scraping app's (HLLAPI or Object X) than run
between 8am  to 5pm.They do a lot of fast reading and writing to the green
screens and then sleep for 3 min's in this cycle all day long.

I believe Im somehow hoging system resources( even on the big iron !)
ie other users interactive reponse time slow down.
What can be done to reduce the load, not knowing anything aboubt
the AS/400 one thing that springs to mind is to create a subsystem
for the Screen Scraping interactive sessions and give them lower
priority.
Am I on the right track here, any ideas welcome.

Thanks Dave