I have a 2005 Lexus gs300. Today while driving the car, it started to drop rpms while in drive.. as I drove further I was not able to get a response from pressing the gas pedal. The car can roll on it's own power nothing else. When I got home I checked the codes and I got a couple codes: P2121, P2127, P2138, P2757. What do I do now should I replace the whole throttlebody?
Based on the results found when searching online for the error codes, it appears that the main issue you're seeing is caused by the throttle pedal sensor, and isn't related to the throttle body.
P2121 - Throttle/Pedal Position Sensor/Switch 'D' Circuit Range/Performance.
P2127 - Throttle Position Sensor E Circuit Low Input.
P2138 - Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.
P2757 - Torque Converter Clutch Press Control Solenoid Control Circuit Performance or Stuck Off.
I'd recommend checking the connection to the sensor to make sure it's securely plugged in and not corroded.
The last code P2757 looks somewhat different though. I don't know how they relate to each other, but one switch being stuck might trigger decreased voltage somewhere else, so checking all the sensors/switches would be good.