Repetition
Hamil,
1. This has been done to death on this forum, but...
2. The TCAS doesn't know if you are a bit heavy today for the altitude (or whatever other excuse/scenario you had in mind), so it may command a climb, and...
3. Even if you ARE a bit heavy/hot/whatever, if you are succesfully in the cruise at FL370, then a pull on the yoke WILL make the aircraft climb. It may not be a lot, it may not be very sporty, and you may not be able to keep it up for long, but you WILL avoid hitting the other guy.
I hope this is a wannabe question, because if you were already flying a 737, you should know this already.