问：换档后汽车停滞不前。

Hi there, the first step would be reading out possible fault codes stored in both the engine computer and transmission computer with a scan tool. Next would be determining the nature under which the stalling occurs. Does it just stall when the shifter is placed in any gear? Or does the vehicle jerk when placed in gear prior to stalling? If the vehicle jerks when going into gear or when coming to a stop just prior to stalling it may be possible you have a torque converter clutch that is not disengaging fully. You may want to enlist the help of a mechanic, like one from YourMechanic, who has the right test equipment to查明问题并进行适当的维修/建议。