Some calling into question Diana Nyad's 110-mile swim

(CNN) -- Diana Nyad inspired the country with her historic Cuba-to-Florida swim, but now, some marathon swimmers are taking a closer look at that feat, and wondering: "Was it too good to be true?"

The record-breaking swim from Cuba to Key West was 110 miles, and 53 hours in shark-infested waters -- and it is now being questioned.

Among other things they want to know: Did Nyad really swim all 110 miles unassisted? Did she rest on a boat? Hold onto a canoe? Was she ever pulled along?

Skeptics speaking to National Geographic and blogging on "The Marathon Swimmers Forum" pointed to one nine-hour stretch when Nyad sped up to more than twice her average speed.

Now, some want Nyad's GPS, surface-current, weather, eating and drinking data released to verify her claim of conquering a swim once considered impossible.

CNN reached out to Nyad's team, who promise a point-by-point response.

An historic swim and lifelong quest for Nyad -- the fifth time is the charm. Now 64, she's tried to conquer the stretch of ocean since she was 29 years old.

Barely able to move, Nyad spoke to CNN's Dr. Sanjay Gupta just hours after her record-breaking feat.

"You know what's great about it Sanjay? It's all authentic. It's a great story," Nyad said.