Is my transmission going out or could it be something else on 99 Escort Wagon?

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My transmission suddenly started refusing to go into high gear. Automatic. When I stopped, it had lost 2 quarts of fluid, blown out under the hood, no leaks visible. The check engine light is always on since I bought it 4 months ago. 197,000 miles. With a quick drive, dealer said tranny was shot. Should it be checked for something else before buying a new transmission? I have read about stopped up filters, etc. When it is supposed to shift to high gear, the engine rpm just revs, but it doesn't shift. This has all happened within a week. The fluid was clear before the loss of fluid, and full.