My dad had an '02 GMC Sierra Denali with 6.0 liter that has been getting a random misfire code. Sometimes it flashes the SES light while driving. So far the fuel and air filters and spark plugs were changed and the MAF was cleaned. Is there a common cause for this or is it going to be a lot of parts replacing? Also, it sounds like it might have a small exhaust leak. Can that possibly cause the misfire?