My 2 cent analysis of Tesla.
The recent volume traded and the announcement that the insertion into the S&P will be in a single tranche is suggestive that the share blocks needed for insertion have already been acquired.
The strong resistance at $600 is probably due to institutional selling via order filling algos (e.g. iceberg) to trim inventory. As a group, the institutions have probably accumulated more stock than is actually required.
The main buyers of Tesla at the moment appear to be retail investors who do not understand the actual insertion process. There appears to be a common misconception that there will be maniac market on close buying, leading to a huge spike in price.
The stock is currently being pumped by the institutions involved in the insertion (e.g. raising price target to $780). This is allow for clearing of unwanted inventory as well as book profits for the insertion. The pumping appears to keep prices firm rather than create a runaway market.
Post insertion, prices are unlikely to rise/fall dramatically due to institutional price control. Prices are likely to remain stable until the next earnings cycle.