Down shifts on an incline and will not shift up

Periodically I will get a "service Engine Light" but the car acts normal. Checked with an OBDII code reader brings up one of two codes: P1698 or P1776.

Also, if driving on a trip and encounter a long grade where the transmission shifts down to a lower gear, the transmission will not shift back up when a level condition is regained. But, I have found if I shift the car into neutral while moving and turn the ignition off and restart the engine - then it drives normal until I pull another hill. Again, the same error codes are read on the OBDII code reader. The codes can be erased and may not return for weeks under normal driving conditions, or until the car sets for a period of time (two to three weeks), or I pull a pretty good incline where the transmission has to shift down.

Responce 1:
I changed the transmission fluid about 500 miles ago when I first experienced the problem, but no change - problem occurred again. P1776 is defined as Solenoid Switch valve In low range position. I think I obtained that definition from Google.