1999 SLS Issues - Running Rough

Hi I am currently trying to help my cousin find out what is wrong with his mom's SLS. The car feel like it is not running on all 8 cylinders to me, just runs rough or wont run at all. I ran the diagnostics and the car came up with these CURRENT codes.


PCM P0420 = Catalyst system Low Efficiency
PCM P0741 = TCC System Stuck off
PCM P1860= TCC PWM Solenoid Circuit Electrical

Anyone know what these codes are referring to? The car threw some History codes to and I will list them if I need to.
Thank you