Typical CPS sensor failure is cutting out when hot and hot restarting until it has cooled down a bit.
Star will do loads more as it will talk to all the other control units not just the engine ECU - if your problem is really gearbox related you may have to go somewhere with star to read the gearbox codes. Might be worth looking in the reccommedations section for someone local to you.
I hope it's not a gearbox problem! I'm sure that's expensive!!
I'm hoping it's not going to cost much to sort out. I just don't understand why it's ok in W mode but not in S! Must be a problem with 1st gear! Hmmm, oh well, I think I'll find a garage with a Star and see what comes up. Is that the best idea??