I had the same exact problem. Rain would make it miss-fire. Even a trip to the carwash would give me a bit of a miss-fire. I have a code reader that measures pending codes as well, and your miss-fire has to be BAD to throw a pending code. (at least in my case..).

I went to AutoZone and got a set of Accel cops for about 33 bucks each, a fresh set of Autolite double platinum plugs, and a crank position sensor. After the install I went right to the car wash, followed by 3 1/2" of rain the next day (of course..) and not one single miss-fire. about 300 bucks and some elbow grease = problem solved. Those back 2 cops/plugs are a b*tch to get out especially with a 4" lift. You don't have to pull the fuel rails but its tight! Don't forget the anit-seize on the plugs either.

Let us know how you make out!