If you have sar enabled then sar(1) can give you useful historical performance data, if I/O appears to be the problem then iostat(1) will give you a picture of I/O performance now. vmstat(1) will give you system performance information now, I like top(1) that shows a process list with the largest resource consumers at the top and mpstat(1) which is multi-processor aware and shows the amount of CPU being wasted by I/O waiting (i.e. memory and disk access).

Take a look at: http://aplawrence.com/SCOFAQ/FAQ_slow.html , UNIX Performance Management and Unix / Linux / BSD Cheat Sheets II for starters.

Which of these commands are available in SCO Unix I am not aware so you will have to give them a go to find out!

P.S. Tis looks interesting: http://williambader.com/museum/dell/scotuning.html