CR10 V2 under extruding and heating up too quickly
This sounds as if you have bought an incorrect heater element, e.g. one for 12&nbsp;V instead of 24&nbsp;V. The CR-10 uses 24&nbsp;V. The 12&nbsp;V cartridge has a lower resistance, so when powered by 24&nbsp;V, the current is much higher and therefore also the heating power ($ {(\frac{24}{12})}^2 = 4 $ times higher). For details on the calculation, the this answer on question: "PID autotune fails 'Temp too high' with 12 V heater cartridge but works with 24 V?". This makes the hotend heat up very fast resulting in a large overshoot. You need to replace the cartridge for one for 24&nbsp;V.



Note that I recently experienced exactly the same problem by mixing up the cartridges see this answer.