2007 ford explorer xlt

Are you getting any codes? This is normally a sign of internal failure in the transmission. When this type of problem happens you have codes P0741, P1714 or P1715. If they are present, the computer has recognized that there is a problem and gone into default mode; letting you use 2nd gear to be able to drive the vehicle 30-35 mph to avoid the engine going over revolutions. The cause of the problem could be solenoids not working properly. Take it to a transmission shop for a check up. Don't forget to ask for a written estimate and a written warranty if you do the job.