The U.S. National Highway Traffic Safety Administration said Monday it has opened a probe into nearly 1.3 million Ford F-150 pickup trucks over reports of an unexpected gear downshift accompanied by a temporary rear wheel lock-up.

Consumer complaints alleged an unexpected transmission downshift to a lower gear while traveling at highway speeds without any prior warning or driver input, followed by the vehicle rapidly decelerating.

Some complaints added the vehicle's rear wheels would lock temporarily, seize or skid during the downshift, leading to loss of control.