Engine Light

I have a 2002 Jeep Grand Cherokee Overland 4.7 V8. Engine light ccomes on every 5 or 6 days. I always get it reset. The problem is that cylinder 6 keep misfiring. The sparks plugs were just replaced. All brand new. Light came on again showing cylinder 6 misfiring. He swapped out spark plug 5 and 6 to see if it was the particular spark plug. The engine light didn't come on but while at another mechanics shop I asked him to hook the diagnostic test to it and even though the engine light wasn't on at the time he could still see that cylinder 6 is reading low. I'm so confused because the engine light is on again 4 days later from going to the second mechanic and I'm pretty sure theres is something going on with the coil as far as cylinder 6 is concerned. I just got this car and my used car warranty doesn't kick in until 3 more months. I expect it to work like a pro and it runs just fine; however, I would like to know what it sounds like so this "cylinder 6 issue" can be resolved for once and for all. Thanks.