check engine light on again, transmission problems?

Sounds like you need a new shop! Depending on what your car is (more info would have been very helpful), that code can set for 1 of 4 reasons. A, the tcc solenoid is defective. B, the computer is having problems. C, the wiring between the computer and solenoid could be rubbed or pinched. D, the Torque Converter Clutch is malfunctioning. The odds of failure usually land in The solenoid or torque converter itself. If they changed the solenoid, so they say, them its pretty darn good odds that it is in the torque converter. If sp, pucker up, cause it will be expensive. Since it is a newer car, the idle should NEVER be tampered with. They either don't know what they are doing, or, they are trying to rope you into more repairs. Even if it is the motor as they claim, they would replace it or repair it, only for you to get it back and have that same code come back. It is fairly simple to diagnose this problem with the right equipment and the right know-how. Bottom line, find someone that knows what they are doing, even if it is a little bit more.

The torque converter lockup solenoid locks both halves of the torque converter together to increase fuel mileage and reduce trans temp during cruise (when not accelerating). When it locks your engine is locked 1:1 to your transmission input shaft. If you are feeling vibration and the engine RPMs are dropping perportional to braking it is not disengaging as it is supposed to as soon as you it the break. Normally the problem is the solenoid itself, did they replace that or just reset the light? Some of these techs are idiots if the computer doesnt tell them there is a problem they dont know what to do.

If its not the solenoid the only other thing i could think of is the boo (brakeon-off switch) maybe its not detecting the break being applied.