Here are the specs for an i5-6500.
https://www.cpu-world.com/CPUs/Core_i5/Intel-Core i5-6500.html
If your CPU is limited to 3200 MHz, Intel Turbo Boost is disabled. If you have an option for this in the BIOS, make sure it is enabled. Also make sure that the core C states are enabled in the BIOS or the CPU will not be able to use maximum turbo boost.
Go into the Power Options and set the Maximum processor state to 100%. A setting of 99% or less will disable turbo boost. It would be a good idea to press the Restore plan defaults button.
Are you using the latest BIOS version? An updated BIOS might solve this problem.
If you are still having trouble, give ThrottleStop a try...