Phil,
It sounds like the carb is slightly too large for the 22 inch prop. Did you try richening the high end a little? Another idea is to not allow the carb to open completely. Many people have trimmed down props to the next lower size. It will give you slightly more pitch at the tip then a stock prop, which will cause some drag. The Zinger Pro has a pointed tip and may not gain much, because of increased tip drag. If you recontoured the prop tip and shaped the airfoil, you would gain the most in my view. A tip cut at an angle like Topflite should work well.

Dave