If it puked fluid out the vent, sometimes it just means it was a little overfull, and no damage was done!
At this point, I'd do the sniff test first. If the fluid is still bright red, and doesn't smell burnt, I wouldn't do a thing. Definitely don't try to add back in what you think you lost.
Long term, I do recommend a Tru Cool Max replacement cooler for any heavy E-series.
Have you ever replaced your radiator? At this age, it's likely not very efficient anymore, and that could contribute to higher transmission temps.
