I had a '93 Cougar that would slip a little if I was taking off from a standstill up a hill. I tried adding another half quart of tranny fluid, even though it was already on full according to the dipstick, and that fixed it. I put another 25k miles on the car before I sold it, and the problem never did come back.
Assuming your transmission was acting okay beforehand, I'd put that additional fluid back in and forget about it.
