There is an adjustment allen screw in the top of the trans that is used to adjust the shift point. The little rubber plug on the top of the trans is where the adjustment is made, pull the plug out & look inside, you have to rotate the spur gear until you see the adjustment nut, use an allen key driver & turn the adjustment nut clockwise to make it shift sooner, don't adjust it to far though, 1/16th a turn then test, repeat again if still not changing soon enough. You need to have the engine tuned reasonably well to as a poorly tuned engine will prevent it from changing, as can to much slippage in the slipper clutch. The trans needs to get to high enough revs to get the change to happen. Even though I have my Revo 3.3 engine tuned nicely, it won't change gears until the engine is warm & running properly. They lean out a bit as fuel starts to get down a bit, under half a tank so the best way to tune them properly is at half a tank of fuel. Tune it to run correctly at half a tank & it will be slightly rich when full & not to lean when near empty.