Cadillac Repair: caddy not in overdrive?, steady speed, engine speed

Question
How can I tell if my 2002 DHS shifts to overdrive during highway driving? What should the RPMs be at 60 MPH on a flat road?

Answer
With the engine at normal operating temperature, maintain a steady speed of 65 miles per hour and while maintaining this speed with your right foot, Slowly apply the brake pedal with your left foot just enough to illuminate the brake lights and watch your tachometer increase in engine rpm's. when you release the brake pedal while still maintaing your speed in about 2 to 3 seconds your tachometr will decrease in engine speed as the over drive re-engages.