Engine power reduced
Your engine cannot perform the way it should. A cause would be the Throttle Positioning Sensor, or the wiring harness may have a broken wire at the plugin. Have the vehicle scanned for trouble codes to verify.
The onboard computer system has sensed a problem with something in the engine management system, you should also have a check engine light along with it, you will need to have the code pulled to find out what has failed or of you have an open corcuit. Someplace like autozone can pull the codes for you free of charge. If your so inclined.
Can a bad O2 sensor cause reduced engine power?
Yes but they usually have a check engine light and a code stating something is wrong with it, could be exhaust restriction or fuel delivery.
The check engine light is on, and I am getting a P0155 error code. This is the Bank 2 / Sensor 1 Heater Circuit Malfunction. Would this cause the truck to go into reduced engine power after the motor was running for a while?
Yes it very could, if it's not heating up properly the readings will be inaccurate and the computer will react accordingly, possibly even going back into closed loop under low speeds, so check the O2 heater circuit, it may have blown a fuse, or the resistance is too high inside the O2 sensor itself. The car is almost 10 years old this fall so you might think about replacing the upstream O2 sensors as a maintenance item, downstream O2 sensors seem to last twice as long as upstream, so don't worry about those until you get a code for them, and even then it might be catalyst and not the sensor.
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