Sounds like you want to set your thread options.
WHM » Service Configuration » Apache Configuration » Include Editor
Under Pre Main Include
Select All Versions and enter:
Code:
<IfModule worker.c>
MinSpareThreads 50
MaxSpareThreads 125
ThreadsPerChild 25
</IfModule>
Edit the numbers as needed. I usually use increments of the ThreadsPerChild value. for the Min/Max.
WHM » Service Configuration » Apache Configuration » Global Configuration
Check that Max Request Workers is set high enough to cover the max number of worker threads you wish to allow.