A thief boosted a bakery truck on the Upper East Side Monday — but instead of selling the $60,000 ride, he dutifully made the regularly scheduled dropoffs along the driver’s route, police sources told The Post.

Wearing only his underwear, David Bastar, 30, of Nanuet stole a Grimaldi’s Home of Bread truck — full of $8,000 worth of baguettes, whole-wheat rolls and loaves of sourdough — on Second Avenue near East 99th Street around 3 a.m., police said.

He then followed instructions mapped out on a piece of paper on the front seat, parceling out the baked goods to at least three restaurants and stores, police and bakery workers said.

“When I heard he actually made a few deliveries, I laughed out loud . . . I guess he really wants to be a truck driver!” a real Grimaldi’s deliveryman said.

Once he was done making real drop-offs, Bastar tossed loaves of bread out the window while zooming down Lexington Avenue, police sources said.

The crook then brought his blue-collar fantasy to Queens, tailing a limo driver over the 59th Street Bridge because, he later told cops, “I thought I had to follow him to make deliveries.”

The chauffeur, Armondo Sigcha, 43, of Guttenberg, NJ, called police around 8 a.m. to report the stalker, he said.

“He was tailing me very, very closely . . . When I’m speeding up, he’s speeding up. When I slow down, he slows down,” Sigcha told The Post, adding that he even made several quick turns to lose him.

“I’m raising my hands to him and saying, ‘What the hell is going on?’ ” Sigcha said.

Rookie Port Authority Police Officer Jason Rando pulled him over on Terminal Drive, opposite La Guardia’s Central Terminal.

Realizing right away that the man was mentally unstable, Rando called an ambulance and Bastar was taken to Elmhurst Hospital’s psychiatric ward, police sources said.

At Queens Criminal Court Tuesday night, he was charged with criminal possession of a stolen vehicle and released into his parents’ supervised care.

His mom, Diana Bastar, said she “had no idea” why her son was fixated on delivering bread.

“I’m speechless . . . He’s been estranged, so I really can’t tell you,” she said.

Deliverers for the bakery called the caper the best thing since sliced bread.

“It’s really so funny to me. I can laugh, of course, because the police caught the guy,” said one truck driver.

Additional reporting by Frank Rosario and Natalie O’Neill