If you have an Aftermarket Turbo and are running more RPM than factory, you will see a few problems if you are still using OEM springs. First is valve float, which can cause serious damage to the valvetrain. Second is intake and exhaust valves can be blown open by boost and exhaust drive pressure which allows reversion. Reversion can hurt your power potential by allowing exhaust gasses to enter the cylinder on the intake stroke. Inert gasses in the exhaust, when re-introduced into the cylinder shield the fuel particles from oxygen in the cylinder. This does a few things that negatively affect power. It increases the time delay from start of injection to start of combustion, it decreases the maximum pressure and maximum temperature reached in the cylinder and it increases the total time needed to completely burn the available fuel. Correct valve spring pressure is a very important piece of power production. If you are running a tuner on an otherwise stock truck with a VGT charger, based on exhaust drive pressure, these springs will help you.