Two codes come up P0115 and P0766?

 Two codes come up p0115 & p0766. Where do I start? I just spent $260.00 for installation of speed sensor last week. Where is the shift solenoid "D" located and approximate cost? Also, the other code suggests hot engine but its running half of the temperature gauge about the middle. The car is new to me and don't know much of its history. It has 2.2 engine if that makes a difference.