Check if you are using the latest BIOS version and latest drivers recommended by Dell. Then, I suggest you to run Intel® Processor Diagnostic Tool. This stress test will tell us if there is anything wrong with the processor.
Intel® Processor Diagnostic Tool (64-bit)
See my CPU performance screenshot below, I don't see anything wrong with yours but if you feel that your system is slow, I would check on any application running on the background, I would run an antivirus and as mikec_intel mentioned before, make sure all drivers are up to date.