ARLINGTON -- For all the Rangers’ splashy free-agent signings and trade acquisitions, their most valuable pitch this season has belonged to their longest-tenured starter: Dane Dunning and his 91 mph sinker.

As the Rangers enter an American League Championship Series showdown vs. the Astros beginning Sunday, Dunning is a big reason why they’ve made it so far.

Dunning's sinker, according to Statcast’s Run Value metric, has accrued the most value of any Rangers pitch this season.

“If you look at the most valuable guy on the staff, [it’s Dunning] because of how he was used this year,” manager Bruce Bochy said in September.

Dunning, a 28-year-old in his third full season in the big leagues, delivered a breakout 2023, with a career-best ERA (3.70) in a career-high 172 2/3 innings. He began the year in the bullpen before slotting in as a starter in May after Jacob deGrom’s torn right UCL required surgery.

But Dunning wasn’t sure if he’d even make the club coming out of Spring Training with all the Rangers’ offseason additions. He said he lost his feel for his sinker to start the season, and he turned to a cutter he had introduced in 2022 but rarely thrown.

“I was getting a lot of weird swings, weird takes,” Dunning said. “And [the cutter] got just a lot more comfortable for me.”

When Ian Kennedy rejoined the Rangers in September, the right-hander learned firsthand just how much Dunning had improved.

Dunning became Kennedy’s catch partner this October. One of Kennedy’s few remaining teammates from 2021, the right-hander impressed Kennedy with the sinker-cutter combo.

“That’s when you really grow to appreciate how good his stuff is,” Kennedy said. “Seeing him pitch, he gets me crossed up when you think he’s going to throw a sinker, and he throws a cutter. [I] can’t imagine being at the plate thinking the same thing.”

For Dunning, it’s all about keeping the hitters guessing. He doesn’t throw any of the pitches in his arsenal much more than a third of the time.

When Dunning added a sweeper last season, he felt like the pitch blended together with his slider too often. So he ditched it this season, instead reintroducing his curveball to the mix.

“I wanted to have distinct pitches that I can throw at any point in time,” Dunning said.

With all the tinkering, Dunning takes advantage of whatever resources he can get.

• Scherzer "ready to go" for ALCS

In the offseason, Dunning joined Tread Athletics, a pitching development program that helped former teammate Cole Ragans with his own breakout campaign for the Royals. Dunning went back to throwing his four-seam fastball, with some convincing from pitching coach Mike Maddux. And he regularly seeks advice from all the additions to the pitching staff, crediting Max Scherzer for helping him with the four-seamer and Nathan Eovaldi with his mechanics.

When it comes to being a new dad -- Dunning’s son Mack was born in May -- he goes mostly to hitters on the team, like Marcus Semien or Travis Jankowski, for advice. And Kennedy.

“He’s got like 14 kids,” Dunning said, joking. (Kennedy has seven children.)

Mack has made it to each of the Rangers’ home games so far. Dunning is hoping that will continue in the ALCS.

After starting most of the season, Dunning will likely return to a bulk relief role behind Andrew Heaney or Scherzer. But he has embraced change, both on the mound and off.

“I did a lot of different things this year,” Dunning said. “I haven’t been playing as much video games. I got rid of social media on my phone -- my wife runs it now if you see any ‘I love my wife’ posts -- just got rid of a lot of background noise.

“I was able to just focus on the task at hand. That’s helped me a ton.”