why not rebalance to your desired asset allocation? If your comfort level and desired asset allocation is with more equities, then buy more. If not, perhaps sell some equities and rebalance into bonds. Market highs are a good time to lock in some gains with a few rebalancing trades, then consider DCAing the amount you rebalanced back into VTSAX. If the market goes down, you've bought new shares on sale. If it goes up, your new shares are worth more and so on.