Q: Can’t reach 55 mph

The issue you are writing in about is common enough that a specific diagnostic, namely a reduced engine power diagnostic is performed by technicians dispatched by YourMechanic. If you request that diagnostic, the responding certified mechanic will get this issue resolved for you. In your circumstance, the vehicle’s powertrain control module (PCM) may have stored one or more diagnostic trouble codes that will identify the "general area" in which the fault lies in the engine management controls. If not, a real time scanner is used to look at actual engine operating data and that will usually reveal enough clues to pinpoint the fault. Although the throttle control system is a common trouble area with reduced power, there are quite a few other components and systems that could come into play and, of course, there is always the possibility of multiple, or "coincident", faults. Here are some of the possibilities that YourMechanic dispatched technicians would consider:

Defective throttle position (TP) sensor
Defective oxygen sensor
Defective accelerator pedal position (APP) sensor
Loose or damaged wiring
Defective throttle body
Defective powertrain control module (PCM) (not typical; ONLY if a long, long list of other possibilities is ruled out)
Any fault/error that will affect drivability function
Any fault/error that will affect vehicle performance
A fault/error in the emissions system
A fault/error in the throttle control system
A fault/error in the transmission control system

If you request the recommended diagnostic the mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.