got a 166/P0720 code from Advanced Auto

If I am correct, this code translates to "The output shaft speed doesn't match the reported vehicle speed" I changed the fluid and filter as a start. Fluid looked good. No metal pieces detected. What should I look at next?

is it possibly the speed sensor?

...yup! :grinyes: Bad speed sensor. Had to reset the 'check engine' light, but problem solved. Total cost : $28 and some change. Changed it myself - easy access on tranny - 5 minutes :)