Transmission problem or just electrical

I have a Dodge G caravan 1996, 150,000 M Transmission rebuilded 3 nonths ago, the problem came on only two weeks ago.
It is allways the same thing . Driving over 45 miles My wipers go on
for one or two times just before the tranny suddenly downshift to 2nd gear and refuse to go any higher. I have to pull over, put it in park, kill the engine, and then re-start it, it works fine for another two o three days. I did a computer scan and I got a faulty transmission relay code, I don't even know where that relay is or if can be a problem in the circuit some where before or after the relay, maybe the BCM .... ? on the other hand the engine light is giving mi a code 12 (Battery disconected recently) but the battery haven't been disconected in a year. At least with the wiper thing I get a warning before happens, so I can slow down, at 80 miles the engine gets in the 7,500 rpm when that happens, can't be good.
I'll appreciate any idea, I'm lost. Thanks
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