When it gets really wet or goes through drive through wash cuts out - then starts after a while but runs really rough.

Does it smooth out as the engine warms and time passes? I had this issue with my 300ZX and although I couldn't solve it due to my running twin open-element filter cones, my suspicion was that condensation on the mass airflow sensing element was causing the issue. It's a hoot wire meter and when cold and damp it'd stumble. As the element warmed it burned off the condensation and the car would smooth out. Maybe that's the issue you're having too?

You need to change your HT leads and your distributor cap. When they get old they are very prone to allow moisture to penatrate and cause the leads and cap to ark causing poor running and starting. Try spraying a moisture repellent (WD40) on the leads and cap then run thru the car wash see if it helps. Good luck.