Carlos Sainz sees Sunday's U.S. Grand Prix as a true test of Ferrari's hopes of winning a first Formula 1 constructors' title since 2008.
Ferrari brought upgrades to their home Italian Grand Prix at Monza on Sept. 1, with Sainz's teammate Charles Leclerc winning and then taking pole position at the following race in Azerbaijan.
Leclerc was on pole in Austin last year, before being disqualified in the race for excessive wear on his car's rear skid block, while Sainz finished third.
Ferrari are third in the constructors' standings but only 34 points behind champions Red Bull and 75 adrift of leaders McLaren with six rounds remaining.
Their car was unstable in high-speed corners earlier in the season but that problem appears to have been resolved, although none of the last three tracks were typical of what is still to come.
Ferrari have still outscored Red Bull in four of the last six races.
"We are coming back to normal tracks with long, combined corners, high-speed corners. Let's see where we are now in these kind of tracks and see if we can still fight like we did in Singapore and Baku and Monza," Sainz told reporters.
The Spaniard said the tracks since Monza had boosted confidence that the upgrades would work everywhere.
"I think this will be the most important test so far for us to see whether all these upgrades that we brought in the past are working in the right direction for more of a normal kind of track like we see here in Austin," he added.
Sainz, who is joining Williams at the end of the season, said there was nothing significantly different on the car for Austin after a front wing upgrade in Singapore.
"It's confirming whether our better pace in the last three races is coming more from going to tracks that really suited us... or whether it's also the upgrades having a big effect on whether we were more competitive in those three tracks.
"Austin will be able to tell us which one of the two it is."