I have a 97 gmc sierra K-1500 with a 5.7. If there is heavy dew, rain, or any kind of moisture it runs really rough. Changed dist.,rotor, plugs, plug wires, ignition coil, and ignition control module and no help, have any ideas.

possibly crank position sensor wires, the wires go on the pass side from by the coil down to by the crank pulley, follow them down make sure they didnt touch the exhaust or chafe anywhere. you can try on a dry day misting water on wires with the engine running and see if it stumbles. slight possibility if you dont find anything that cheap parts may not be liked by this engine, delco or delphi stuff is usually recommended, especially the cap the way it is its easy for the power to arc across on the cheap ones

Fill a spray bottle with water, and at night when it is dark spray a mist all around the engine compartment (engine running) when it is dark outside. If you see blue sparks anywhere that is the source of your problem.

First thing that comes to mind is the MAF.
Do you run a K&N air filter by chance?
I have heard of some cases where high humidity, or rainy days, could cause an over oiled K&N air filter to release oil, which too much of it on the MAF'* hot wire can cause the car to run rough.

When it is dry/hot are there any similar problems?
Or do they seem to go away when dry/hot?

Thank you for the suggestions. I will try them all and see what happens as soon as I get the chance. WilliamE, it seems like it runs fine when dry and hot or at least not as noticeable.