1994 Ford F-150 engine mis fire

I have an F150 that misfires in wet or even in humid weather. It's so bad skipping the car check engine light comes on and the truck won't move without bucking and eventually stalling. Of course I have already replaced all of the usual stuff like wires, plugs, distributor cap and rotor, air filter. I've checked the coil connections and that seems ok.

It runs pretty decent in dry conditions but I still detect a little loss of power and skipping on occaission.