If you look at the 2016 NRMP PD survey for Pulm/Crit, grades from medical school were of minimal importance. Only 30% of PDs said they use them when deciding who to interview, and they had the lowest ranking of importance on the list (3.4). When deciding who to rank, only 14% considered medical school grades and those that did ranked them of similar unimportance.
The most important things for fellowship are
grad status (USMD vs DO vs IMG, as well as tiers within that), prestige of residency program, performance during residency (i.e. PD letter), other LORs (and phone calls, etc), and research. According to the PD survery, ~50% of programs also use USMLE filters.
And once you get an interview, personality fit and specific interest in the program seem to also be extremely important.
https://mk0nrmpcikgb8jxyd19h.kinstacdn.com/wp-content/uploads/2017/02/2016-PD-Survey-Report-SMS.pdf