2004 Jeep Cherokee throttle pressure sensor

My jeep was having an issue that I noticed one day on the interstate. It seemed as if it was either stuck in the passing gear or the overdrive was stuck off. While stuck in this postion it would not let me engage my cruise control. It just seemed like it needed to hit the next gear. I only notice this when I am going over 55 mph, all other speeds seem to be running in the right gear and at the correct rpm. The codes that come up when I call them up on my odometer ar p-0123 and p-0121 - they both talk about the throttle pressure sensor and its voltage. ( One says tis to high and one says its to low) I am guessing that is what is causing the issues with my rpms and crusie conrol. But not knowing ANYTHING about the T.P.S. I am looking for some advice and maybe aomewhere to find out how to install a new if that is what is neccesary. Thanks for helping !