Engine reving too high, temperature gauge in the red.

Hi, my 2007 Ford Explorer XLT, 4.0, 6 cyl just turned 32,000 miles. when driving under normal conditions at any speed the engine will suddenly begin to rev up, but the speed does not increase, as if you were driving and dropped the car into neutral while keeping your foot on the gas. Sometimes when this happens (but not all the time) the radiator temp gauge will jump from the middle (normal) temp position up to the red (danger) area, then the temp overheat warning light will come on. this will last for about 10seconds then all goes back to normal. What is wrong with my truck? Thank you.