CPU wait state

I have been experiencing a problem on a Compaq system, GS140, running TruUnix64 5.1 Rev 732.
It’s been patched to latest version.
I am testing with GZip because it is the simplest way to recreate the problem, but this occurrs with any type of continued processing. On something as simple as a Gzip there is a delay of 10 seconds before the processor starts the Gzip, then with multiple Gzips there is a degradation of cpu processing so that in the end, caching has filled up and the cpu goes intoa zero wait state and pretty soon it takes longer and longer for the any process to get CPU time.