I'd recommend checking to see that the heatsinks are clear. I was having horrible slowdown on a 2010 MBP that I realized after a lot of hair pulling was due to

I'd recommend checking to see that the heatsinks are clear. I was having horrible slowdown on a 2010 MBP that I realized after a lot of hair pulling was due to thermal issues. Pulled the fans/heatsinks, there was a solid mat of dust between the fans and heatsinks. Cleaned those up, and suddenly the fans never even spun up to audible levels.