Does your motherboard's BIOS support that processor? Is your power plan set to High Performance?
As noted it sounds like your mobo either does not support this model CPU or you need to update the BIOS for proper support of this CPU. The only means a BIOS has to set the correct CPU vcore voltage and frequency is if it can identify the CPU model on boot up. An older BIOS will not have the information for newer CPU models and thus will set the CPU vcore and frequency to a lower speed based on whatever reference or safety design is implemented in the BIOS. You may need to use your old CPU to update the BIOS. After you update the BIOS be sure to clear CMOS before you install the newer CPU model so the BIOS scans all hardware and sets the appropriate BIOS settings for proper operation. If the info. provided is too confusing you may desire to have a local PC repair shop or PC friend do the BIOS update.