P0742 is a TCC Stuck ON code and typically happens from a clogged up TCC solenoid but can be a number of other things also. I have info on this on my info page in the link in my sig. Replacing the solenoid often helps the problem BUT debris is the cause more times than not as this solenoid rarely fails on its own so a new solenoid is just going to do the same thing down the road. The trans will definately feel terrible when the code sets. It can be a tricky problem to tackle and the majority of the causes are torque converter slippage or over-pressure problems that can be fixed by upgrading a few parts, but once the damage is done it generally means a new torque converter, valve body, and possibly other parts.
From Trannyman himself.