2003 Tracker will not turn over when parked on an incline

Are you saying, it cranks good but won't start or it won't even crank? If a starter motor problem, I'd have to check wiring circuits. It might be best to set your parking brake before you shift into park, that way the brake holds the vehicle and not the tranny. The only other thing I could think of would be a fuel issue of some kind, depending if front of vehicle is up-hill or down?