1994 J30 misfire/rough run primarily in wet conditions

[kakrunch]

I bought a used J30. It misfires SOMETIMES and occassionally starts hard. It tends to happen ALOT more when its raining or damp air. It seems to come and go, but will get somewhat better at high rpm's. I put in new plugs, new fuel filter, and used cleaner on the mass airflow sensor. No change. Bought a new coil and tried it on all of the cylinders, no help. Used injector cleaner for 3 or 4 tanks and it seemed to help some for awhile. I only run premium gas ( a buddy told me these need premium gas).

Any ideas?

 

[kakrunch]

Update. For other reasons I had the timing belt, water pump, and battery replaced. car sat for a month during this process. When I got it back it ran great for 2 weeks, then started the same issues. WHAT GIVES?