Cashner, who missed most of spring training with a sore right biceps, has won two of his past three starts.
"Tremendous job by him today," Rangers manager Jeff Banister said. "He continues to get stronger with every outing."
He's throwing harder, too.
"Early in the season I was still looking for strength," he said. "The last outing I had some (velocity) and it was definitely there today in some big spots."
Cashner (2-4) gave up one run and five hits. The right-hander had been 0-9 in 18 road starts since September 2015.
"The biggest thing for Cash today was the ability to go up and down with the fastball, in and out with the fastball, and back it up with the changeup-curveball combo," Banister said.
Cashner is 10-31 with a 4.83 ERA in 110 road games, 62 starts.
Toronto had won five in a row.
"We just couldn't get anything going against Cashner," manager John Gibbons said.
Gallo hit an opposite field solo shot to left off Joe Biagini (1-3) in the fourth, his eighth homer in May.
"It was out of the zone," Gallo said, "but if I can get a good swing on it, I'll take it."
"This big guy can hit a ball out of any part of the ballpark, foul pole to foul pole," Banister said.
Elvis Andrus had three hits and scored twice as the Rangers improved to 9-18 on the road.
Making his fifth start since joining the rotation earlier this month, Biagini allowed two runs and seven hits in a career-high six innings. His seven strikeouts were also were a personal best.
"It was important for me to see myself be able to handle the workload," Biagini said.
Texas tied it in the third when Andrus singled and stole second before coming around on Jonathan Lucroy's two-out single. Andrus added an insurance run when he scored on Dominic Leone's wild pitch in the seventh.
Toronto went 0 for 7 with runners in scoring position against Cashner, who has held opposing batters to a 3-for-39 (.077) mark in such situations.
MANY HAPP-Y RETURNS
Blue Jays LHP J.A. Happ (elbow) arrived in the clubhouse following the game and was scheduled to throw a bullpen session, indicating he could be activated to face Cincinnati on Tuesday. Happ made his first rehab start with Class A Dunedin last Thursday, allowing three runs and seven hits in three innings.
Toronto's Devon Travis extended his hitting streak to 12 games with a single in the fifth. He's batting 22-for-48 (.458) over that stretch.
Blue Jays: LHP Francisco Liriano (shoulder) was scheduled to make his first minor league rehab start for Triple-A Buffalo on Sunday night. ... 3B Josh Donaldson and SS Troy Tulowitzki returned to the lineup after getting the day off Saturday.
Rangers: Texas returns home Monday to begin a three-game series against Tampa Bay. LHP Martin Perez (2-5, 3.77) threw a season-high 113 pitches in his previous start, his highest total since undergoing elbow ligament replacement surgery in 2014. RHP Erasmo Ramirez (3-0, 3.00) starts for the Rays.
Blue Jays: RHP Marcus Stroman (5-2, 3.30) starts the opener of a three-game interleague series against Cincinnati. Stroman is 4-0 with a 2.95 ERA over his past seven starts. RHP Lisalverto Bonilla (0-2, 6.17) starts for the Reds.
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