2004 Freestar w/3.9L...parked outside in driveway (not in garage)...

Rained Sunday night; got in the van to leave for OH Monday a.m.; drove a couple miles, but it wouldn't shift out of 2nd. Switched to the old Jeep (for 530 miles; not as nice!)...

Drove it again when we got back; engine started normally and ran smoothly; still wouldn't shift out of 2. Reverse engagement is smooth, and 1 and 2 feel normal, but never goes to 3 or above. After a couple of miles, it started pinging lightly and the "Check Engine" light started flashing.

I've hard trouble with water in the PCM on this van before. I went through the whole TSB on sealing the areas where water supposedly gets into the PCM and the trans vent. I thought that was supposed to solve the problem...anyway, I think it's probably the same thing. I found another TSB that tells how to take the cover off the PCM and seal it up. I'll try that one...

My questions:
1. Ford says about water getting into the transmission vent; what are the symptoms of this?
2. Any tips for doing a better job than the TSB at keeping water out of the PCM?

Thanks.