I don't know if you have transbrake solenoid like mine, but ours has removable valve, and spring. We mostly race Heritage JrFuel racing a 2 tenths Pro-tree, but when we race B/ND in Comp on a 5 tenths full tree, we put in slower releasing valve and weak spring to try and keep our driver from Red-Lighting.
So check your valve and spring [ go stiffer if you want it faster] One issue you need to know is with a slow transbrake is once you release your button, the motor free wheels until the brake comes into play, and what that means is if you are using a two-step, and you have a 4000 chip in the two step, the motor can climb to 5600+ before it hits the tires. So if your tires go-up in smoke you might want to run a higher chip and a quicker valve/spring. It's a real balance.
Or your valve is just hanging up. Also check your switch and ground wire.
Jon Hansen