I bought the truck last week and as I have been driving it I notice that the truck has an issue going up hills and accelerating. When accelerating the truck does not change gears at the proper time and sometimes by taking my foot off the gas the gear will change. The same issue happens when the truck is going up hill and this causes me to not exceed a speed of 45 mph going uphill. The power steering also cuts out occasionally while driving and the AC does not work. On top of this there is a check engine light with a code that indicates that I have a faulty O2 sensor. I was wondering if the power loss issues are attributed to this.
The O2 sensor has many codes associated with the sensor itself. Some codes can indicate that your engine is running lean and alternatively some can mean that your engine is running too rich. The power steering and A/C have pressure switches that are known to cut out the power steering assist and the A/C compressor under heavy load conditions.
Your transmission may not be shifting correctly due to the engine not running correctly. You may also have a problem with the injection or fuel system alongside the issues of the transmission, A/C, and power steering. My best advise would be to have the vehicle assessed by a certified tehcnician, such as one from YourMechanic, to properly diagnose your loss of power and make the necessary repairs.