I dont care what anyone says, LT's vs stock manifolds with aftermarket mid pipe, LT's win everytime.
What they're really trying to say is...their panties are in a bunch because they spent $1000 or more to have headers installed and only gain 25hp.
Its not like the LT's are making you lose power, so how are they a waste of money?
You aren't going to gain 25 hp over an off road mid pipe. The restriction is in the mid pipe and not the headers. The OEM manifolds flow very well.
Please see site below
http://kennebell.net/KBWebsite/Common/pdfs/header_cat_xpipe_exhaust_tests.pdf