my duramax's intake temps are mostly above 150 degrees this time of year. What can I do to keep it from sucking hot undehood air? I am not ready to pay $400 for an intake.

Vararam and others make cheap ones that help. Check with the Vendors here for who sells what.

Used ones are also found in the For Sale Forum. There are also some home brewed mods that help. A little searching will find these.:)