I ordered these plugs after reading articles on the GM truck forum. The previous reviewer is correct that they come with a .040 clearance and the factory clearance is .060. After reading the truck forums it states that due to the design of the plugs they need to be installed as is with a 0.040 gap. After installing it, I didn't notice much of a difference until I went on my usual weekly commute. On a freeway trip, my truck (2005 GMC 5.3) was looking for a transmission while going up a steep hill on cruise control. After these plugs, my truck could easily climb hills without going out of overdrive. I've also increased my gas mileage by at least 1 mpg. My truck had 90,000 miles on it when I changed the spark plugs and wires (MSD from Amazon BTW). I also strongly recommend replacing the wires as they can be easily damaged when removed. Do yourself a huge favor and buy these items together for more power/savings and easier plug replacement; http://www.amazon.com/gp/product/B000AL8VD2/ref=oh_details_o02_s01_i00http://www.amazon.com/gp/product/B0014ZVSVK/ref=oh_details_o02_s01_i01http://www.amazon.com/gp/product/ B0006HPA02/ref=oh_details_o02_s00_i00