Ok, I know it is not recommended to mix and match memory modules, but I hate to waste money on replacing existing components.  I just upgraded my 8GB T3630 i5-8600 CPU@3.10GHz workstation, which had an existing 8GB 2666 memory module, to 32GB.  I used 3 Crucial memory modules, which have identical specifications to the originally shipped Dell memory.  Now the BIOS is reporting a memory speed of 2400 instead of 2666.  This is frustrating.  Is there a solution, or do I need to buy another Crucial module to replace the Dell module, or do I have to return the Crucial memory because it isn't compatible at 2666?

All modules Dell and Crucial are spec'd at:

DDR4 PC4-21300 • CL=19 • Unbuffered • NON-ECC • DDR4-2666 • 1.2V • 1024Meg x 64 • CAS latency - 19