She was voted GOAT and seems to be beloved around here. But arguably there is reason for suspicion:
1. It's widely believed that epogen use was extremely common in the early and mid 2000s, when Kastor was in her prime. That alone is cause for suspicion, since it would be very difficult for a clean runner to beat Epogen-using elite runners. A cloud looms over every very good performance between the mid 1990s and late 2000s. And Kastor's marathon AR (run near the ehight of the epogen era) was a very good performance.
2. In the early 2000s, she trained in the same group as Teddy Mitchell, who subsequently moved to Albuquerque. There Mitchell trained withddy Hellebuyck and coached marathoner Deeja Youngquist. Both Hellebuyck and Youngquist were subsequently busted for epogen use.
Obviously there is not enough evidence to show that Kastor was doping, but I think it is foolish to dismiss the possibility.
Related:
https://sportsscientists.com/2017/05/recalibration-world-records-brief-thoughts/
http://www.drmichaeljoyner.com/how-believable-are-running-records/