What is running at "Half what it used to?"
Dino and Syn oil wouldn't cause this by themselves otherwise they wouldn't sell it as a pre-made combo.
What else was done at the same time?
Is it mis-firing?
Base oil is just that. What twin said. Ground, ocean, desert, it's the same oil. Additive wise is the syn. So there is no way oil is going to light up an engine and make it run bad? Leave the new oil alone. Change spark plugs. How long since they were change? It's more coincidence that this occurred.