The GM 120 is a nice bit of kit. However because of the flexibility that is offered in the programming firmware, its pretty easy to screw up a motor if you set it incorrectly. The majority of the parameters should not be played around with. In essence, if you dont know what it means, then leave it well alone.
What firmware do you have on the speedo ?
Some useful info is offfered on this thread .........
http://www.rctech.net/forum/electric...shless-74.html