I know this is not for a Hummer. but it is all the brand name after market filters for a duramax, with independant test results. The same brands make filters for the hummer. Check it out, it is good reading, and really shows that the aftermarkets flow more air, and it shows the cost of it also.
http://home.stny.rr.com/jbplock/ISO5011/SPICER.htm