SPX broke the trend line with a gap. Time to sell rallies?

Since April, the SPX has risen around 15%, and since November's low, it has increased by almost 40%.
This is quite significant for such an index, making us wonder if this rise is fundamentally justified (in my opinion, it is not).

But, as they say, "trade what you see, not what you think".
What we saw was a strong upward move.
However, keeping this expression in mind, we also observed a breakdown with a gap yesterday, which was not filled during the day, indicating a "gap and run."

My preferred strategy for the index is to sell on eventual rallies above 5500, with a target at 5250.
This strategy would be negated by a new all-time high (ATH).