Hi Lee
My suggestion would be that its the gear ratio you currently have on it. I just looked at the final drive ratio for the Mi2 and with the gearing you have you get either a ratio of 8.14 or 9.59. Only reason there are 2 ratios is because there was a choice of lay shaft pulleys, 17 or 20 teeth.
I have never used one of the losi systems but with my Novak system I am currently running a ratio of around 6. I know some of the other guys are running similar gearing too.
If you are at racing tonight I can lend you a different pinion to try if you want, so long as you are running 48dp
I hope this helps
Jon