Spark plugs can last over 80,000 miles. 5 months means nothing to them. Also, you probably should mention not to over-torque the nuts down, because you could easily pull up some studs from the valve cover. I think the torque is somewhere in the 20s, and what I do is just hand tighten while pushing down on the coil pack, then give the nut a good 1/2 turn with the wrench. Anymore and you may have problems.