BS..oem are still restrictive, and aftermarket cats will set off your warning light beacuse they do flow better, but not that efficient at cleaning the unburned gases.

I have monolythic cats on my Silverado, took them off and gained 2 mpg. so you can't tell me the monolythics are non-restrictive. this is worth the cost of materials, if you added up your fuel bill before and after for the year especially at $3.80-$4.00 per gallon, 2MPG adds up, so it's all gain, even if you make 5 extra hp.