99 subaru AT OIL TEMP light?

i have a 1999 subaru outback station wagon. i started it up and drove it to work this morning, cold start and no warmup time. about 4 maybe 5 miles into the drive my AT OIL TEMP light is blinking. never done it before. started the car up after i was done at work, and it did not come on. i looked up some info online and most places say its the auto transmission fluid. i had the transmission flushed and refilled back in february since i blew a tranny seal/gasket and the fluid was old. the route is a stop and go style and theres a good amount of steep grades, but i did not go up any steep grades much today before the light went on, maybe a couple hundred feet.should i see a mechanic immediately or not?