VCore lowering drastically (momentarily) on high CPU load

[[TC]»Elmo«]

Sounds like the CPU thinks its getting too hot and is throttling back to prevent damage.

Quick search found me this: "Maximum operating temperature 55°C"

I'd take a look at the state of the cooling - make sure there's no dust, check there's good airflow in the case etc. If it's still a problem, try getting some thermal paste (Arctic Silver 5 is good), and re-seat the cooler.
If that doesn't help much, I'd consider getting a better cooler (assuming you're still using the stock AMD one)