The Mopar ’24 Jeep Gladiator—as the automaker refers to it—packs an array of add-ons, from rock rails to a tonneau cover, and it gets flashy red accents and a host of special decals and badges.

The Jeep Gladiator sounded like a winner on paper: a meshing of two wildly popular things: a Jeep Wrangler and a pickup truck. But the Gladiator failed to ignite the anticipated demand ...