My very first thought was; 3 teeth is a lot! My 2nd thought was; what is the competition running for a gear ratio?
My 3rd thought was; where are they pulling you? Is it through the corners, or down the straight, or both? If it's a both, changing gears is not likely to help. And again, 3 teeth is a lot! There's so many things that could be happening, it's really hard to say what the problem, and the solution, is. It could be that your engine just doesn't make enough horsepower. There are differences in horse power output even in box stock classes. It could be your set up, your jetting, your stagger, your timing, your spark plug, your fuel or maybe others. More, and more detailed, information would be helpful.
You know, if you could find out what the other drivers are doing, and then just copy them, it might help. It wouldn't hurt to ask some questions, as long as you're aware that the answers to your questions may not be exactly right. lol