Sounds like the tranny is fried from all the low fluid levels and topping it off again if it is hard to move and the fluid level is correct. Did you check it after you arrived home and see it was still full? Look for an obvious leak in the form of a puddle. Is it under the front bumper area of the Monte or under the engine area somewhat behind the front wheels. Could be something as simple as a tranny cooler line fitting loose at the radiator or a broke fitting at the transmission. Something pretty persistent if your adding fluid everytime you drive it.
I have a tranny from my 02 Monte Carlo SS with about 60,000 miles on it I would sell you for about $200 plus shipping. That might get your Monte back on the road again. I never had a problem with it and had the fluid changed at about 40,000 miles. I'm in Utah. Best of luck, if it is in pretty decent condition and you owe a year on it still, could be worth keeping.......