As it was explained to me. Transmissions out of the factory are made to shift smoothly through the gears for a smooth ride. A solenoid valve makes that happen, however, that typically causes the clutch plates to ware out from the slow transition between gears over time. Rebuild mechanics will often install a solenoid to make that transition faster, therefor making the clutches last longer. That's your bump. And, yes, it is more prominent when it's cold and tapers some when warmed up. Even when warm, if you accelerate quickly from a full stop you will feel a good bump as it shifts quicker than the stock transmission. The only real problem with it is it seems a little ******* the rest of the drive train behind it, such as, the u joints. Other than that, it should last ya a while. Hope this helps.
