[Bigdav160]

Is the MIL on? If the trans is not shifting when the computer wants it to it will likely set a code.

edit: I remember two vehicles that were brought to me with shifting problems but no codes and in both cases found the shift solenoids were not properly seated with the retaining clip inserted into the o-ring groove.

Really, you need a good scan tool and look at the data to see if what you think is a problem is normal operation.