Race car mystery-Help us solve PLEASE

How did the driver know "something happened"? Did the car drop it's nose? Did he see a gage or hear something? Did he not notice until he got the time slip? Were the incrementals on before the 600' mark?
If the leakdown was good, the physical parts are good, then you have either fuel or spark. My experience is like Lenny - once a convertor breaks the stall speed goes through the roof or it slips in high gear and sounds like a supercharger. Inspect the MSD - especially the advance system(s). Wet flow the fuel system to make sure it's maintaining pressure. That is a lot so something went away. Direction from the driver would help discern what it was.