Cash out or keep Pension

Hi all! I have a pension fund from the 5 years I was with the first company I worked for out of college. It looks like upon retiring, I would receive a whopping ~$400/month = $168,000 if I retire at 65 and live another 35 years. I am currently 31 and considering cashing out the pension to invest in index funds etc. Any thoughts on this / things to consider especially when it comes to taxes? Thanks!