I am going to assume you have the 4 speed auto. These are well known to self destruct.
Water may have gotten into one of the plugs on the tranny and shorted. You can also drain the trans fluid and replace, inspect the fluid and magnet on the pan for metal shavings.
Also, your valve body may be shot, this is the cheapest fix just shy of a new trans. There are plenty people that are or were in the same boat... maybe they will chime in...
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