Code P2757?

Thats a transmission code for a faulty torque converter pressure control valve its inside the transmission.

Which one is it slu ?

Its typically the one closest to the bell housing or (torque converter) toward the front of the transmission mounted on the valve body.

Usualy let gets that way because of a worn transmission over all or dirty oil or just naturally worn out over time or all of the above that said ,often times if you go to all the trouble of taking the pan of and going in there the other solenoids and the filter are also changed at the same time for good measure sometimes if one goes the others are right behind it...they can be purchased as a whole set and i highly recommend changing the oil every 2 years after that and keep a close eye on it in between. It is just the nature of automatic transmissions. "Good luck ".