The AT has its own ECU. What error code(s) are stored? It's nothing but superstition to replace ATF if a light is blinking because of a dirty switch contact. When the shifter cable is adjusted properly, and the shifter detents are well-aligned with the switch detents, the switches tend to be self-cleaning and long-lived.

As tonyg stated, AT failures are rare. Thus the advice to switch to synthetic is overkill. The advice to flush yearly (20K-30K mi) is overkill. The advice to do both is off the charts... Do not expect any mileage increase beyond a tiny fraction in cold weather: it will flow easier right after startup so the tiny pumping burden will be less, but unlike engine oil, increased slipperiness is not present nor desirable in synthetic ATF, which must be 'grabby'.

- Dave; '95 854T, 147K mi