One major problem: points leader Jimmie Johnson was fast, too. Johnson had the second-quickest lap around Homestead-Miami Speedway on Saturday and had the fastest 10-lap average.
"We're just working on comfort," Johnson said afterward. "It's different conditions now than what we'll have during race time, so we're being smart about our changes."
Kenseth reached 171.980 mph around the 1 1/2-mile oval, just ahead of Johnson's 171.647. Defending series champion Brad Keselowski was third, followed by Martin Truex Jr. and Kevin Harvick.
The 10-lap average is often a better indicator of the top cars. Johnson averaged 167.905 mph over his first 10 practice laps.
Johnson, Kenseth and Harvick are the only drivers still in contention for the title. Johnson enters Sunday's finale with a 28-point lead over Kenseth. Johnson needs to finish 23rd or better to win his sixth title in eight years.
Johnson has seven top-five finishes in nine Chase races this season, the kind of closing success that makes a tough task nearly impossible.
Kenseth was tied with Johnson three weeks ago, but pit trouble at Phoenix last week diminished his chances. Still, Kenseth's crew chief, Jason Ratcliff, believes staying close with one of the most dominant programs in NASCAR history says a lot about their team.
"I prefer it's them over anyone actually," Ratcliff said after the final practice. "It's more of a challenge for us and it's setting the bar very high. Coming into the last few races knowing that we are really close and going head-to-head with these guys week in and week out, I'm ecstatic that it's those guys and we're going to continue to work hard to not only achieve what they've done over the last seven, eight, nine years, but hopefully surpass that.
"I think if everybody's goal in this garage area is not to do that, then they should find something else."