How do you know it has only been leaking for the two miles or so that you're referring to? How do you know it hasn't been leaking for quite some time and possibly leaking coolant into the transmission? Did your mechanic drop the pan to confirm/deny the presence of coolant in the transmission?Could a small leak and less than 2 miles driving damage it?
Just looking at the dip stick won't tell you anything as the lighter transmission fluid will sit on top of the heavier coolant/radiator fluid, all other things equal.
I agree w/ those who suggested a rebuild, or at least start preparing for one...And if your radiator is found to have been leaking coolant into the transmission, it's likely completely shot in that if I were the one working on your vehicle, I'd send your existing transmission to the scrap yard (assuming it's fully contaminated w/coolant) and build you another, entirely different one out of my inventory of cores.