WHISTLER, British Columbia — Shauna Rohbock is trying to solve a mystery at the Vancouver Olympics, but time is running out on the 32-year-old pilot for Team USA's top bobsled.Rohbock says she cannot find the right sequence for turns 4 and 5 at Whistler Sliding Center's super-fast course."I don't know, I just keep falling out and hitting the walls," she said.Rohbock, a Mormon from Orem, Utah, and former BYU soccer star, and brakeman Michelle Rzepka in USA-1 are in sixth place after Tuesday's pair of runs.__IMAGE1__USA-1's time of 1 minute, 47.09 seconds is 0.89 seconds off Canada's top sled, in first place entering Wednesday's final two runs with a time of 1:46.20.The U.S. has three sleds in the top six. Rohbock and Rzepka are tied with Bree Schaaf and Emily Azevedo in USA-3. Erin Pac and Elana Meyers in USA-2 are in second place.GER-2 is in third, 0.49 seconds ahead of the two USA sleds in sixth.Rohbock, who won a silver medal in Torino four years ago, expressed frustration with the turns earlier in the week during practice.Little changed when USA-1 took its first two runs in competition."Just a really bad 4-5," Rohbock said. "You know you're into the flat section there, it's hard to get your speed back. I've just been struggling with it all week. Nobody really has a clue there. We keep trying different lines, and they're just not working out."Rohbock and Rzepka posted the second-best runs in Saturday's training and the fifth best on Sunday. The pair did not take its last two training runs Monday."I had options to take runs (Monday), but I didn't take them," Rohbock said. "I needed to rest. That many days in a row is pretty hard on your body."Rohbock, a member of the National Guard Outstanding Athlete Program, has won on the Whistler track before. She took home gold in a World Cup race in February 2009."Shauna's got it," Rzepka said. "She's a very talented driver. I have complete faith in her. We have two more runs Wednesday."But Rohbock was less optimistic than her partner."I'd have to have two very good runs (Wednesday) and hope that somebody else messes up," she said.USA-1 was in seventh place after its first run of 53.73 seconds. The sled's second run was faster, at 53.36.