Police said the truck's rear sliding door was padlocked and been hammered shut with more than 10 fortified nails to keep the woman from escaping.
Dallas police have arrested a man on suspicion of locking a disabled woman in the back of a moving van in 100-degree heat.
Police said they suspected the 21-year-old woman would be dead if she had spent another minute locked in padlocked truck.
"She was distraught, disoriented, soaking wet and apparently near death," Senior Cpl. Janice Crowther said.
Police said she was dehydrated and suffering from heat exhaustion when police and fire-rescue workers discovered her Monday afternoon.
"I'd been in there about an hour," she said.
Harvey Ray Moss, 50, was arrested Monday night on charges of injury to a disabled person and assault.
The woman's family said she has the mental capacity of a 10-year-old. With her family's permission the woman, who did not want to be identified, spoke about the abuse she said Moss inflicted on her for several years.
"He hit me with a broom, a stick, a mop, all types of stuff," she said.
She said Moss, her boyfriend of three years, locked her in the back of the truck as punishment.
"He forced me to stay there," she said.
When the woman's family did not hear from her for several days, they called police.
Investigators discovered the truck parked outside a Pleasant Grove house where Moss once lived.
Neighbors and even police veterans said they could not believe a woman was locked inside.
Police said they had to break into the truck, because the rear sliding door was padlocked and been hammered shut with more than 10 fortified nails to keep the woman from escaping.
Police said Moss locked her in with fresh wounds from what appeared to be his initials carved into her flesh. The woman told NBCDFW.com he used a coat hanger to brand her name into her leg.
"Oh, it's one of the most disturbing abuse cases of the mentally ill I've seen in a long time," Crowther said.
Moss is being held in the Dallas County Jail on a $50,000 bond.
The woman was treated and released from Baylor University Medical Center at Dallas.