I'm glad you asked. No, it isn't! If you haven't heard of the Barbell Logic podcast, I would recommend checking out the podcast on this very subject. I believe it's called something like "switching from stronglifts to Starting Strength".
To give you the cliffs, just start the next workout at 3x5 at whatever weight you are currently using for 5x5, or potentially an extra jump in weight, normally 5 lbs for lower body and 2.5 lbs for upper body, for the first Starting Strength workout.
Normal caveats apply, which are that you need to be eating and sleeping enough as well as have 95% perfect form in order to perform LP correct. If you haven't already, pick up a copy of the blue book. Good luck, dude!