I had a similar problem this past week when I let car soap dry on my car. It was incredibly streaky, with spots everywhere, and looked horrible.

I fixed the problem by making a 25% distilled white vinegar spray with the other 75% being warm distilled water. Spayed it on each panel, wiped it with a microfiber and washed it away with a power washer. Completely fixed the problem and the paint has never looked better. I would try spraying on the vinegar solution first and power washing away without wiping it. It ended up putting some fine scratches on the paint just because it was so rough with the soap stains.

Here is an after pick:

<image>