When i got my rc18t from sneako on here his ESC would do some weird throttle problem. It'd act as if i still had my finger on the throttle for another second even though i took it off. I changed my esc, problem goes away. Chances are your either your esc isn't allowing voltage to flow through good for some reason or your connectors may be slightly loose. With problems like this it could be the stupidest of things, so don't throw out the stupid things until you've tested them to make sure it isn't that.

Hope this helps you.