My Elantra jacks 1 minute into the startup and you can hear the sound and feel the jacking at this point, the car finds it difficult to run from idle. Seems like it gets stuck at gear 3.
Runs fine when on a straight road but when I apply the brake, it struggles to pick at 1.
Won't climb upward unless I restart the car, 30secs, I hear the sound and the whole process reactivates. ​​sometimes I hear that sound and jerk when I manually change gear from park to reverse or drive.

An engineer said its solenoid, another said its ECU and solenoid (brainbox not supplying to the solenoid)

Kindly help me as I am already getting two opinions from different engineers.