I had virtually identical shifting 2-1 slam and got failsafe and when I read the codes it said it was solinoid error.
It was a dirty cannon plug at transmission. I'm sure that's what your problem also was.
Did you ever have the symptom of dash indicator not match the gear selector?
I did not figure out how water got into that connection since the rubber boot is definitely water tight. It almost felt like the water comes down the inside of the wire bundle so I left my rubber boot open for now so any new water can drip out.
I plan to fill the boot with silicone and figure out some seal for the connector which may not have one. (or if I determine water does come from under the hood through the wire bundle I'll cut a weep hole and the silicone in the boot will force it to drop out not go into the connector.
About 1/2 oz. of very rusty water came out of my connector when I removed it !