My brother has a 03 HD with a 6.0. He put one of them K&N filter kits on it, the complete kit. It seems to run good without a load but when loaded down it really sucks. It is bogged down for some reason, and has trouble finding the gear when it needs too. Even when in tow/haul mode. Does he need a exhaust system too? Seems like it just isn't breathing good enough. Anyone have the same issue?

Kurt,

To be honest.. I am guessing that your brother got the filter thinking that it was a better option for his truck.. if you check the AC Delco filter is a better filter than the K&N...

Long read .. but here it is
http://www.dieselplace.com/forum/showthread.php?t=10372&highlight=filter+study

K&N crap, If the filter was over oiled, it will dirty the MAF sensor(tell pcm how much air engine is intaking). Will need to clean VERY CAREFULLY. Some use electronic part cleaner is the only spay you can use.

6.0 do respond nicely to a turbo or radix S/C

I also have to agree....that is just not true. I have 40k on a 5.7L LT1 Impala SS and frankly, 8100Hammer's post is way more possible...I've read that linked post in detail and frankly, it did concern me until I realized I had 40k on one of those K&Ns and that the car is at 82k now, not burning a lick of oil and running so smooth, you could balance a bunch of wine glasses on the top, full of your fav beverage and not spill a drop (vehicle not moving of course).

Sound like to me that you do not have big enough cam in that impala ss.

Yea, I haven't messed with the cam (yet). I was thinking of putting in the hot cam with some 1.6 rollers, but then I was towing with this thing and realized at 305hp, I'm still doing pretty good....then again, too much is never enough. :)

If the filter was over oiled, it will dirty the MAF sensor(tell pcm how much air engine is intaking). S/CSo do you think that is what the problem is? The filter is oiled, would it be best not to oil them?

Theres a difference between oiling them and over oiling. Oiling them is essential to proper filtration.