Yamaha has struggled to match Honda around the Texan venue ever since the two teams held a private test there in March.
As Honda duo Marc Marquez and Dani Pedrosa secured first and second places in qualifying on Saturday, Lorenzo was 1.079 seconds adrift in third place.
But the world champion is convinced Yamaha is steadily improving.
"It is a difficult weekend for us at the moment," Lorenzo said. "But we still have the grand prix tomorrow, and it's a long race.
"The feeling we have is not perfect. The track has improved so much, and now we can ride it more or less like a normal track, but there's still not the last bit of performance, especially not for the Yamahas.
"We are trying to modify the bike to get more grip. Qualifying was not so bad, but the pace of the Hondas was impossible for us."
Despite that gap, Lorenzo thinks it could be possible to turn the tables over a race distance.
"I think in the race anything is possible," he said. "It's a very long race. We are convinced we can have a good race tomorrow."