Shifting problems with my 1999 Ford tarus

. Disconnect the negative battery cable overnight, in order to force the computer to "relearn" shift points. If necessary, record radio code first.

. Drop and clean the transmission pan, change filter, and refill with Mobil 1 Synthetic Multi-Vehicle ATF. Change fluid and filter every 30,000 miles. The automatic transaxle is the weak link in most FWD vehicles.

The link below should help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-5.html#post552241

This is the procedure I follow on my 2000 Taurus, with the 3.0L Duratec engine. It's a great, reliable, and under-rated car, especially for the money. If you haven't been changing the fluid and filter every 30,000 miles, your problem may be more severe (e.g. worn clutch packs) and require a rebuild.