I buy my own PPO health plan, and once again need to change insurance companies because of steadily rising premiums.

The application asks for a complete medical history. If I leave anything out, can they realistically go back and search my history for surgeries, doctor's visits, etc. that I have not listed?

The insurance company will ask what drs you have seen and for what condition. Any time you go to the dr after you become effective they can check that drs records for any time you had seen them previously. If you go to a new dr you won't have any history with them to be checked.

They are looking for pre-existing info as some companies will deny all prex unless it is stated in your application.

Your best bet is to be completely honest because if they find out you were seen for a condition that you didn't declare on the application they can request $ back for claims paid.