Beer

Replaced the PCM a couple weeks ago. It was flashed by the parts supplier.
Did the passlock relearn procedure and got the van to start with no issues.

When I first drove it, it started shifting hard. It was difficult to even feel when it shifted before the PCM replacement. It doesn't shift into drive. Stays in third. Now I'm getting about 11.3MPG instead of the 15.7-16.3 I normally get. Gives 3-2 shift solenoid code
I'm also getting a random cylinder misfire.

No check engine light before the replacement.

The van only gets driven on the weekends. We had several days of constant rain. The van wouldn't start. No issues when it was parked. It would crank and try to fire, but wouldn't catch. PCM was soaked, as usual. Took it apart and there was all kinds of corrosion inside the module.

Any ideas on what to check? I'm thinking I need to have the PCM reflashed. I'm not sure if there are any other relearn procedures other than the passlock.

2000 Express, auto, 5.7L