+1
On your servo being weak I run a 3305 in my losi and it stops on a dime. If I am not mistake a 3305 is about $60 bucks spend the extra $20 and get you a Ace 1015 digital. linkage setup is also a source of throttle brake problems. Even once you get a better servo work on your linkage.
I would not use 250 grit sandpaper more like 1000 grit is best. 25o grit takes of to much per stroke. You want to sand it down the least amount possible to achieve the desired effect. You can always sand it a little more with 1000. You can never put back on what you've taken off.